Let be an increasing continuous function on the entire real line, and let be its inverse function. The function satisfies the following conditions:\begin{center}\fbox{\begin{minipage}{0.9\textwidth}(A) For ,(B) For ,\end{minipage}}\end{center}For a real number , let denote the number of intersection points between the line of slope passing through and the curve . Suppose that is discontinuous at and with . Evaluate(Here, you may use .) [4 points]\
[THOUGHT] The problem asks for the evaluation of an expression involving , where is the number of intersection points between the line and the curve . The function is the inverse of , which is given piecewise.
First, let's determine the explicit form of . Since is increasing, must also be increasing. Condition (A): For , . Taking the square root, . Since , , so is negative. Thus . So . Since is increasing, it must pass through the origin (or near it) and preserve sign. Let's check . . For , must be positive because is increasing and . So for , . For , let where . . Since is increasing, must be negative for . So . Thus, for , . Let's check the derivative to ensure it's increasing in this interval. . For , , so . Then . So it is increasing. At , . At , .
Condition (B): For , . Since is increasing: For , must be positive and greater than . . Check continuity at : Limit from right is . Value from left is 2. Continuous. Check derivative for : . Increasing. For , must be negative and less than . . So . Check continuity at : Limit from left is . Value from right is -2. Continuous. Check derivative for : . Increasing.
So is defined as:
The problem involves the intersection of the line and the curve . The line passes through . Let's analyze the intersection in the -plane. . The line equation is (for ). If , . Since (because is not 1? Wait. . So . The line passes through . is not 0. Let's check . . So is on . . So is on . The line passes through fixed point . This point is NOT on the curve . We are looking for the number of solutions to . Let be the variable on the curve . Alternatively, let's switch to the -domain (which is the domain of ). Let be the variable. . The intersection condition is . So we need to find the number of roots for the equation . Let . Then we are solving , or . Wait, we need to be careful with . . From the definition of : For , . If , then . Let's check roots. is not in interval. . Actually, let's use Python to analyze the function and find the range of values of . The number of intersections corresponds to the number of times the horizontal line intersects the graph of . However, we must handle the vertical asymptote where . Also, consider the case separately. . . So is a solution if . Yes. So is always a solution for any ? . Equation: . So is a solution ONLY if . Wait. The equation is . If , LHS=0. RHS = . So . So for , is not a solution. So we can analyze for and .
Let's define . We need to plot or analyze to find the number of solutions for a given . The values of where is discontinuous are the local extrema of or asymptotic values. The problem states is discontinuous at and with . This suggests there are two critical values of . I will use Python to:
- Define .
- Define .
- Find critical points of (where derivative is zero).
- Find limits at infinity and at vertical asymptotes.
- Determine and .
- Calculate the required expression.
The expression is . Note: is the number of intersections. and are likely the local maximum/minimum values of .
Let's start coding. [/THOUGHT] [PYTHON] import numpy as np import sympy as sp
def f_inv(y): if y < -1: return -np.exp(-(y + 1)) - 1 elif -1 <= y <= 1: return 2.5 * y - 0.5 * y**3 else: return np.exp(y - 1) + 1
def K(y): val = f_inv(y) if val == 1: return np.inf # Handle division by zero return y / (val - 1)
Let's use sympy to find exact derivatives and critical points
y = sp.symbols('y', real=True)
Piece 1: y < -1
f1 = -sp.exp(-(y + 1)) - 1 K1 = y / (f1 - 1)
Piece 2: -1 <= y <= 1
f2 = sp.Rational(5, 2) * y - sp.Rational(1, 2) * y**3 K2 = y / (f2 - 1)
Piece 3: y > 1
f3 = sp.exp(y - 1) + 1 K3 = y / (f3 - 1)
Derivatives
dK1 = sp.diff(K1, y) dK2 = sp.diff(K2, y) dK3 = sp.diff(K3, y)
print("Derivative Piece 1:", sp.simplify(dK1)) print("Derivative Piece 2:", sp.simplify(dK2)) print("Derivative Piece 3:", sp.simplify(dK3))
Solve for critical points where derivative is 0
crit1 = sp.solve(dK1, y) crit2 = sp.solve(dK2, y) crit3 = sp.solve(dK3, y)
print("Critical points 1:", crit1) print("Critical points 2:", crit2) print("Critical points 3:", crit3)
Also need to check the values at boundaries and asymptotes
Asymptote is where f_inv(y) = 1.
In piece 2: 2.5y - 0.5y^3 = 1 => y^3 - 5y + 2 = 0
roots_asymp = sp.solve(y**3 - 5*y + 2, y) print("Asymptote roots (Piece 2):", [r.evalf() for r in roots_asymp])
Check limits at infinity
lim_inf_neg = sp.limit(K1, y, -sp.oo) lim_inf_pos = sp.limit(K3, y, sp.oo) print("Limit y -> -inf:", lim_inf_neg) print("Limit y -> +inf:", lim_inf_pos)
Check values at boundaries y = -1 and y = 1
val_neg1 = K(-1) val_pos1 = K(1) print("K(-1):", val_neg1) print("K(1):", val_pos1)
[/PYTHON]
[THOUGHT] Let's analyze the function to determine the number of intersections . The function determines the value of for a given . We are looking for the number of values for a given . The domain of is all real numbers. Let's break down the behavior of in different regions.
Piece 1 (): . . Derivative is zero at . . So . Let's evaluate . . Note that . . . Since , . Limit as : (from positive side, since numerator is neg and denom is neg). At : . So in this region, goes from 0 up to and then down to . Wait, let's check the sign of derivative. Numerator of derivative is proportional to . At , large positive. At , negative. So it increases then decreases. Max at . Local max value .
Piece 2 (): . . Roots of denominator (asymptotes): . From Python output: . Inside , the only root is . Let's call this root . So there is a vertical asymptote at . Let's check behavior around . . Derivative . At , deriv is negative. So for , denom is positive. For , denom is negative. Numerator is . For , num > 0, denom > 0. . For , num < 0, denom > 0. . For , num < 0, denom < 0. . Values at boundaries: . . . Derivative of in this region: From Python: . Critical points where . So is a critical point? Let's check derivative at : . Yes. Is it a local extremum? For (close to 1), , deriv < 0. So is decreasing. So at , we have a local minimum? Wait, for , . As , (num negative, denom negative small). So decreases from to . So is a local minimum with value 1. For : . . Derivative zero only at (not in this sub-interval). So decreases from to at , then decreases to as . Wait, check derivative sign. is negative for . So derivative is always negative in . So decreases from to .
Piece 3 (): . . Derivative: . Zero at . For , , so derivative is negative. . Limit as : . So decreases from to .
Summary of graph:
- : Increases from 0 to (approx 0.425), then decreases to (approx 0.333).
- : Decreases from to . (Passes through 0 at ).
- : Decreases from to .
- : Decreases from to .
Let's collect the ranges covered by (which corresponds to ):
- Region 1 (): Range . Max is . End value .
- Region 2a (): Range .
- Region 2b (): Range .
- Region 3 (): Range .
Let's visualize the number of solutions for a given . We draw the horizontal line and count intersections with graph of .
- : Only intersects Region 2a. (1 solution).
- : is a solution. Also limits at are 0. But only at . (1 solution).
- :
- Region 1: Intersects twice (once going up, once going down).
- Region 2a: Intersects once (between -1 and 0).
- Region 3: Intersects once.
- Total: 4 solutions.
- :
- Region 1: Intersects once (at boundary? No, is boundary. . In Region 1, value approaches at boundary. In Region 2a, starts at . So is one point).
- Region 1 peak is . So there is another intersection in Region 1.
- Region 3: Intersects once.
- Total: 3 solutions.
- :
- Region 1: Intersects twice.
- Region 2a: No intersection (max is 1/3).
- Region 3: Intersects once.
- Total: 3 solutions.
- :
- Region 1: Tangent at peak (1 solution).
- Region 3: Intersects once.
- Total: 2 solutions.
- :
- Region 1: No intersection.
- Region 3: Intersects once.
- Total: 1 solution.
- :
- Region 2b: Minimum at . Value 1. (1 solution).
- Region 3: Starts at 1. (Continuous at 1). So is the point.
- Total: 1 solution.
- :
- Region 2b: Intersects twice? No, monotonic decreasing from to 1. So 1 intersection.
- Region 3: Max is 1 (at boundary), decreases to 0. No intersection for .
- Total: 1 solution.
Wait, let's re-verify the monotonicity in Region 2b. decreases from to 1. So for , there is exactly 1 solution in . So for , . At , (at ). For , (in Region 3). So is constant 1 for . Wait, is ? . . Yes.
Let's check discontinuities. values:
- : 1
- : 1
- : 4
- : 3
- : 3
- : 2
- : 1
- : 1
- : 1
Discontinuities are at:
- : jumps from 1 to 4.
- : jumps from 4 to 3.
- : jumps from 3 to 2, then to 1.
Wait, let's trace carefully. Range of Region 1: . Range of Region 2a: . Range of Region 2b: . Range of Region 3: .
Let's sum the number of solutions for each interval of :
- :
- R1: 0
- R2a: 1
- R2b: 0
- R3: 0
- Total: 1
- :
- Total: 1 ()
- :
- R1: 2 (values go 0 -> max -> 1/3. Since , any value in is hit twice)
- R2a: 1 (values go 1/3 -> 0 -> -inf. Hits once)
- R2b: 0
- R3: 1 (values 1 -> 0. Hits once)
- Total: 2 + 1 + 1 = 4.
- :
- R1: 1 (at , value is 1/3. But wait, R1 is . Limit is 1/3. R2a is . Value is 1/3. So is the solution. It counts once.)
- But does R1 hit 1/3 again? R1 goes . If , it hits 1/3 somewhere else?
- . . Yes. So there is a solution in where .
- So R1 contributes 1 solution strictly inside, plus the boundary .
- R2a starts at (at ). So is the solution.
- R3 contributes 1 solution ().
- Total: 1 (inside R1) + 1 (boundary) + 1 (R3) = 3.
- :
- R1: 2 solutions.
- R2a: 0 solutions (max is 1/3).
- R2b: 0.
- R3: 1 solution.
- Total: 3.
- :
- R1: 1 solution (peak).
- R3: 1 solution.
- Total: 2.
- :
- R1: 0.
- R3: 1.
- Total: 1.
- :
- R2b: 1 (at ).
- R3: Limit is 1. is the solution.
- Total: 1.
- :
- R2b: 1.
- R3: 0.
- Total: 1.
So discontinuities are at:
- (1 to 4)
- (4 to 3)
- (3 to 1)
- (constant 1? No, 1 to 1. Continuous?)
Let's check . Left limit (): 1. Value (): 1. Right limit (): 1. So continuous at .
Discontinuities are at , , . The problem says "discontinuous at and with ". This implies exactly two discontinuities. Let's re-evaluate . Limit is 1. Value . Limit is 4. So discontinuous at .
Now check and . At : Left limit 4. Value 3. Right limit 3. Discontinuous. At : Left limit 3. Value 2. Right limit 1. Discontinuous.
So there are 3 discontinuities? . The problem says "discontinuous at and ". Maybe one of them is not a discontinuity? Or maybe I miscounted solutions. Let's check . . Is it possible that ? No. Is it possible that ? No.
Let's re-read carefully. "Suppose that is discontinuous at and ". This implies ONLY two points. Let's check the case again. is always a root for . For , we found 4 roots. For , we found 1 root. Definitely discontinuous at 0. So .
Now between and . Maybe is not discontinuous at one of them? At : : 4 solutions. : 3 solutions. : 3 solutions. Jump from 4 to 3. Discontinuous.
At : : 3 solutions. : 2 solutions. : 1 solution. Jump from 3 to 1. Discontinuous.
Why would the problem imply only two? Maybe my analysis of Region 1 max is wrong? . Derivative zero at . Let . . . . So . . . Max value: . Is it possible ? . . . They are distinct.
Is it possible I missed a region? : Range . : Range . : Range . : Range .
Let's re-evaluate the overlaps. Intervals of where solutions exist: R1: R2a: R2b: R3:
Summing up counts: For : R2a (1). Total 1. For : 1. For : R1 (2) + R2a (1) + R3 (1) = 4. For : R1 (2) + R2a (1 boundary) + R3 (1) = 4? Wait. At : R1 intersects twice? . Yes. One intersection is at . The other is inside . R2a intersects at . So is counted in both R1 and R2a? No, is a single point. So we have:
- One root in R1 (strict inequality ).
- One root at .
- One root in R3. Total 3 roots. Wait. Limit : 4 roots. Limit : For : R1 has 2 roots (since ). R2a has 0 roots (max is 1/3). R3 has 1 root. Total 3 roots. So at , jumps from 4 to 3. So it is discontinuous.
For (): R1 has 1 root. R3 has 1 root. Total 2 roots. Limit : 3 roots. Limit : R1 has 0 roots. R3 has 1 root. Total 1 root. Discontinuous.
So we have 3 points of discontinuity: . Why does the problem say and ? Maybe is not considered? "For a real number ..." Usually is slope. Maybe the domain of is restricted? No. Maybe I should check the point again. At : R2b has min 1 at . R3 has sup 1 at . So is the solution. For (close to 1): R2b has no solution. R3 has 1 solution. Total 1. For : R2b has 1 solution. R3 has 0 solutions. Total 1. So is continuous at . Correct.
Is it possible that is not a discontinuity? No, jump from 3 to 1. Is it possible is not? Jump from 4 to 3.
Could and be and ? If so, what about 0? Maybe the question implies and are the only discontinuities? Or maybe and are positive? "Suppose that is discontinuous at and with ." This phrasing usually implies these are the only ones. Let's re-read condition A. . . For , . So . . is increasing. . For , . So . For , . So . So for all . This matches my derivation.
Let's check the derivative at . . Derivative: . At : . Left side: . Derivative: . At : . So is differentiable at . This means the curve is smooth at . The function . At , . . . At : Num = . Denom = . . So is smooth at and decreasing. So passes through with non-zero slope. This means takes values slightly above for and slightly below for . Wait. In Region 1 (), goes up to then down to . In Region 2a (), goes down from . So is NOT a local maximum. It is just a value passed through. Wait. Region 1: . ends at . Region 2a: . starts at and decreases. So around , is decreasing. Values of for near : : . : . : . So as we vary across : For (slightly):
- Intersection in R1 (since goes up to then down to . So it crosses twice? No. Let's look at the shape of R1 again. Increases from 0 to Peak, then decreases to . So for , there are 2 intersections in R1. For :
- Intersection in R1? No, values are . Wait. R1 values are in . Does it cover ? Yes, it starts at 0. So R1 covers on the increasing leg. On the decreasing leg, it goes from Peak to . So for , R1 has 1 intersection. For , R1 has 2 intersections. At , R1 has 1 intersection (on the increasing leg) plus the boundary point? No, the boundary is . So for :
- One intersection in R1 (increasing leg).
- One intersection at . Total 2 from this part.
Now R2a. Starts at , decreases to . For : 1 intersection. For : 0 intersections.
Now R3. . Always 1 intersection for .
Let's sum again. Case :
- R1: 1 (increasing leg). Decreasing leg is .
- R2a: 1.
- R3: 1.
- Total: 3.
Case :
- R1: 1 (increasing leg).
- Boundary : 1.
- R3: 1.
- Total: 3.
Case :
- R1: 2 (one increasing, one decreasing).
- R2a: 0.
- R3: 1.
- Total: 3.
Case :
- R1: 1 (tangent).
- R3: 1.
- Total: 2.
Case :
- R1: 0.
- R3: 1.
- Total: 1.
Case :
- Total 1.
So the counts are: : 1 : 1 : 3 (Wait. At Peak it is 2). So constant 3 for . At : 2. For : 1.
Let's re-verify discontinuity. : 1. : 1. : 3. So discontinuity at .
Discontinuity at . Jump from 3 to 2 to 1. So .
Are there any other discontinuities? At , I found counts were 3, 3, 3. So continuous. Why did I think 4 before? I thought R1 went meant it covered twice. But the decreasing part is . It does NOT go below . So for , the decreasing leg has no solution. Correct.
So the discontinuities are exactly at and . We need to evaluate: . . . . First term: .
. . We need . . We know . So . . So . Squared: . Second term: .
Total expression: .
Let me double check everything.
-
formula. : . Correct. : . Correct. : . Correct.
-
behavior. : goes . . : goes . : goes . : goes .
-
Counts. : Only R2a intersects. (1). : is root. (1). : R1 (increasing leg): 1. R1 (decreasing leg): 0 (values ). R2a: 1 (values ). R2b: 0. R3: 1. Total: 3. : R1/R2a boundary: 1. R1 (increasing leg): 1. R3: 1. Total: 3. : R1 (increasing): 1. R1 (decreasing): 1. R2a: 0. R2b: 0. R3: 1. Total: 3. : R1: 1 (tangent). R3: 1. Total: 2. : R1: 0. R2b: 0. R3: 1. Total: 1. : R2b/R3 boundary: 1. Total: 1. : R2b: 1. Total: 1.
Discontinuities: : 1 -> 3. (Jump). . : 3 -> 2 -> 1. (Jump). .
Calculation: . Limit is 3. Term 1: .
. . Term 2: .
Result: 11.
Wait, I should check if . . . Yes, . Also check if . . Yes.
One detail: "Suppose that is discontinuous at and ". Is it possible there are more discontinuities? My analysis shows only 0 and Peak. At , continuous (1 -> 1 -> 1). At , continuous (3 -> 3 -> 3). So exactly two discontinuities.
Let's verify the calculation. . Let . Then . . . From , . So . . Squared is 4. Correct.
Is there any ambiguity about at ? Line passing through with slope 0 is . Intersection with . . So is the only intersection. So . Limit : We found 3 solutions. Limit : We found 1 solution. So discontinuous.
Is there any ambiguity about at ? is the local max of for . At this max, the line is tangent to the curve (in the transformed space). So 2 intersections merge into 1. So count drops by 1. From 3 to 2. Then for , count drops to 1. So discontinuous.
Final check on the question phrasing: "Evaluate ." . . . Limit is 3. Product 3. . Factor 4. Product 8. Sum 11.
One potential pitfall: Is defined on the entire real line? Yes. Is continuous? At : . . Yes. At : . . Yes. Is increasing? Deriv of : : . : . : . Yes, strictly increasing. So is strictly increasing and continuous.
Is it possible that is infinite? No, has finite solutions. Is it possible is vertical? No, is a real number.
What if is negative? . R2a range is . So for any , there is exactly 1 solution in R2a. R1 range . No solution. R2b range . No solution. R3 range . No solution. So for . Limit is 1. . Limit is 3. So discontinuity is confirmed.
What if is something else? Could there be a discontinuity at ? : R1: 0. R2b: 0. R3: 1. Total 1. : Total 1. : R2b: 1. R3: 0. Total 1. So continuous at 1.
Could there be a discontinuity at ? : R1: 1. R2a: 1. R3: 1. Total 3. : Total 3. : R1: 2. R2a: 0. R3: 1. Total 3. Wait. Let's re-check . is slightly larger than . R1 range is . . . So . R1 equation has 2 solutions. One on increasing leg (value in ). One on decreasing leg (value in ). Wait. Decreasing leg goes from Peak down to . So values are in . If , it is in the range. So 1 solution on decreasing leg. Increasing leg goes from 0 to Peak. If , it is in range. So 1 solution on increasing leg. So R1 has 2 solutions. R2a range . If , no solution. R3 range . If , 1 solution. Total: .
Now . . R1 increasing leg (0 to Peak). is in range. 1 solution. R1 decreasing leg (Peak to 1/3). is NOT in range (values are ). 0 solutions. R2a range . is in range. 1 solution. R3 range . is in range. 1 solution. Total: .
At : R1 increasing leg: 1 solution. R1 decreasing leg boundary (): Value is . R2a boundary (): Value is . These are the SAME point . So 1 solution at . R3: 1 solution. Total: .
So is continuous at . Value is 3. This confirms my previous deduction that is not a discontinuity. So only 0 and are discontinuities.
Double check the calculation of . . R1: Tangent. 1 solution. R3: 1 solution. Total 2. Correct.
Double check limit . . small positive. R1 increasing leg (0 to Peak). in range. 1 solution. R1 decreasing leg (Peak to 1/3). not in range? Wait. Decreasing leg values are in . If is small positive (close to 0), it is NOT in . So R1 decreasing leg has 0 solutions. R2a range . in range. 1 solution. R3 range . in range. 1 solution. Total: . Correct.
Wait, did I say 4 before? "Case : R1 (2) + R2a (1) + R3 (1) = 4." Why did I think R1 had 2? R1 goes . Increasing leg: . Covers . Yes. Decreasing leg: . Does NOT cover . So for small , R1 has only 1 solution. Ah. Let's re-verify the range of R1. . . . Max is Peak. So values start at 0, go up to Peak, go down to . So the range of values is . However, for a given value , how many solutions? If : Increasing leg covers it. (Since ). Decreasing leg (from Peak to 1/3) does NOT cover it. So only 1 solution. If : Increasing leg covers it. Decreasing leg covers it. So 2 solutions. If : Increasing leg covers it. Decreasing leg ends at it. So 2 solutions? One at . One on increasing leg. If : 1 solution.
So for : R1: 1 solution. R2a: 1 solution. R3: 1 solution. Total 3.
So limit is 3. . Discontinuity at 0.
For : R1: 2 solutions. R2a: 0 solutions. R3: 1 solution. Total 3.
So is constant 3 for . Then drops to 2 at Peak. Then drops to 1.
So is continuous at ! My previous manual count was wrong, but the correction confirms continuity. Count is 3 for and 3 for . So is: 1 for . 3 for . 2 for . 1 for .
Wait. . Limit is 3. Discontinuous at . . Limit is 3. Limit is 1. Discontinuous at . So .
The calculation remains: . .
Wait, is for ? R2a range . Covers negative values. 1 solution. R1 range . No. R3 range . No. So yes, 1.
Is ? is solution. Are there others? . R1 limit is 0. No solution. R2a passes through 0 at . R3 limit is 0. No solution. So only . Yes, 1.
So the jump is 1 to 3. Limit is 3. . Term 1: 3.
Term 2: . Factor 4. Term 8. Sum 11.
Everything seems consistent.
One check: Is it possible has other extrema? Python found critical points: Piece 1: . (The Peak). Piece 2: . (Local min at boundary). Piece 3: . (Local max at boundary). So no other internal extrema. Asymptote at . Behavior around asymptote: : . : . This matches R2a going to and R2b coming from . Consistent.
Final Answer seems to be 11.
One small detail: "For a real number ..." Is it possible is such that the line is tangent at the inflection point? No, tangency corresponds to extrema of . We handled the extrema.
Is it possible is undefined? No. Is it possible and are not and ? The problem states is discontinuous at and . My function is:
Discontinuities: At 0: . (Discontinuous). At : . (Discontinuous). Everywhere else constant. So exactly two discontinuities. .
Calculation: .
One sanity check on . . R1: 1 solution (tangent). R2a: 0. R2b: 0. R3: 1 solution. Total 2. Correct.
One sanity check on limit . small positive. R1: 1 solution. R2a: 1 solution. R3: 1 solution. Total 3. Correct.
One sanity check on . . . . . . . Correct.
Final result 11.
One thought: Is it possible that has a value different from 1 for ? . R2a: . Range . Monotonic? Derivative of : . For , . . Numerator negative. Denom positive. Derivative negative. So strictly decreasing. So for any , exactly 1 solution. So for , 1 solution. Correct.
Is it possible that has different value for ? R2b: . Range . Derivative negative. Strictly decreasing. So for , exactly 1 solution. R3: . Range . For , 0 solutions. So for , total 1 solution. Correct.
So the function is fully characterized. 11 is the answer.
[/THOUGHT] [THOUGHT] The number of intersection points is determined by the number of solutions to , where . Based on the analysis:
- For , .
- For , .
- For , where , .
- For , .
- For , .
The discontinuities are at and . We need to evaluate .
-
. . . First term: .
-
. . . Squared: 4. Second term: .
Total sum: . [/THOUGHT]
\boxed{11}