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] To solve this problem, we need to analyze the function ( f(x) ) and its inverse ( f^{-1}(x) ) based on the given conditions. The goal is to find the values ( a ) and ( b ) where the number of intersection points ( g(m) ) is discontinuous, and then compute the specified expression.
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Understand ( f^{-1}(x) ):
- For ( |x| \leq 1 ), ( 4(f^{-1}(x))^2 = x^2(x^2 - 5)^2 ).
- For ( |x| > 1 ), ( |f^{-1}(x)| = e^{|x| - 1} + 1 ).
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Find ( f(x) ):
- Since ( f ) is increasing and continuous, ( f^{-1} ) is also increasing and continuous.
- For ( |x| \leq 1 ), solve for ( f^{-1}(x) ): [ f^{-1}(x) = \pm \frac{x(x^2 - 5)}{2} ] But since ( f^{-1} ) is increasing, we take the positive root: [ f^{-1}(x) = \frac{x(5 - x^2)}{2} ]
- For ( |x| > 1 ), ( f^{-1}(x) = e^{x - 1} + 1 ) (since ( f^{-1} ) is increasing).
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Find ( f(x) ):
- For ( x \leq 1 ), ( f(x) ) is the inverse of ( f^{-1}(x) = \frac{x(5 - x^2)}{2} ).
- For ( x > 1 ), ( f(x) ) is the inverse of ( f^{-1}(x) = e^{x - 1} + 1 ).
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Find ( g(m) ):
- ( g(m) ) counts the number of intersection points between the line ( y = m(x - 1) ) and ( y = f(x) ).
- Discontinuities in ( g(m) ) occur when the line is tangent to ( f(x) ).
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Find ( a ) and ( b ):
- Solve for ( m ) where the line is tangent to ( f(x) ).
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Compute the expression:
- Evaluate ( g(a) \times \left(\lim_{m \to a^+} g(m)\right) + g(b) \times \left( \frac{\ln b}{b} \right)^2 ).
[/THOUGHT] [PYTHON] import sympy as sp
Define the variables
x, m = sp.symbols('x m')
Define the inverse function f^{-1}(x)
def f_inv(x_val): if abs(x_val) <= 1: return (x_val * (5 - x_val**2)) / 2 else: return sp.exp(abs(x_val) - 1) + 1
Define the line equation: y = m(x - 1)
line = m * (x - 1)
Find the points of intersection between y = f(x) and the line
We need to find x such that f(x) = m(x - 1)
Since f(x) is the inverse of f^{-1}(x), we can write:
f(x) = y where f^{-1}(y) = x
So, x = f^{-1}(y) and y = m(x - 1)
Substitute y into the inverse function:
x = f^{-1}(m(x - 1))
For |m(x - 1)| <= 1:
x = (m(x - 1) * (5 - (m(x - 1))**2)) / 2
For |m(x - 1)| > 1:
x = exp(|m(x - 1)| - 1) + 1
To find the number of solutions, we can analyze the equation numerically or graphically.
However, for the purpose of finding discontinuities in g(m), we look for tangency conditions.
For |x| <= 1, the equation is:
x = (m(x - 1) * (5 - (m(x - 1))**2)) / 2
Let's expand and solve for m:
2x = m(x - 1)(5 - m^2(x - 1)^2)
This is a nonlinear equation in x and m.
For |x| > 1, the equation is:
x = exp(|m(x - 1)| - 1) + 1
This is also nonlinear.
To find the critical m values where g(m) is discontinuous, we need to find m where the line is tangent to f(x).
This requires solving for m where the system has a double root.
Let's consider the case where |x| <= 1:
The equation is 2x = m(x - 1)(5 - m^2(x - 1)^2)
Let u = x - 1, then x = u + 1
2(u + 1) = m u (5 - m^2 u^2)
2u + 2 = 5m u - m^3 u^3
m^3 u^3 - 5m u + 2u + 2 = 0
u(m^3 u^2 - 5m + 2) + 2 = 0
This is complex to solve analytically, so we might need to find m numerically.
Alternatively, we can find the derivative condition for tangency.
The slope of f(x) must equal m at the point of tangency.
The derivative of f(x) is 1 / (derivative of f^{-1}(y)) where y = f(x).
For |y| <= 1:
f^{-1}(y) = y(5 - y^2)/2
derivative of f^{-1}(y) = (5 - y^2)/2 + y(-2y)/2 = (5 - y^2 - 2y^2)/2 = (5 - 3y^2)/2
So, f'(x) = 1 / ((5 - 3y^2)/2) = 2 / (5 - 3y^2)
At the point of tangency, f'(x) = m, so:
m = 2 / (5 - 3y^2)
Also, y = m(x - 1) and x = f^{-1}(y) = y(5 - y^2)/2
Substitute x into y = m(x - 1):
y = m(y(5 - y^2)/2 - 1)
y = m(y(5 - y^2) - 2)/2
2y = m(y(5 - y^2) - 2)
2y = 5m y - m y^3 - 2m
m y^3 - 5m y + 2y + 2m = 0
y(m y^2 - 5m + 2) + 2m = 0
This is the same as before.
Let's solve for y when m = 2 / (5 - 3y^2):
Substitute m into the equation:
y( (2 / (5 - 3y^2)) y^2 - 5(2 / (5 - 3y^2)) + 2 ) + 2(2 / (5 - 3y^2)) = 0
Multiply through by (5 - 3y^2):
y(2y^2 - 10 + 2(5 - 3y^2)) + 4 = 0
y(2y^2 - 10 + 10 - 6y^2) + 4 = 0
y(-4y^2) + 4 = 0
-4y^3 + 4 = 0
y^3 = 1
y = 1
Then, m = 2 / (5 - 3(1)^2) = 2 / 2 = 1
So, one critical point is at m = 1.
For |y| > 1:
f^{-1}(y) = exp(y - 1) + 1
derivative of f^{-1}(y) = exp(y - 1)
So, f'(x) = 1 / exp(y - 1) = exp(1 - y)
At the point of tangency, f'(x) = m, so:
m = exp(1 - y)
Also, y = m(x - 1) and x = f^{-1}(y) = exp(y - 1) + 1
Substitute x into y = m(x - 1):
y = m(exp(y - 1) + 1 - 1) = m exp(y - 1)
But m = exp(1 - y), so:
y = exp(1 - y) exp(y - 1) = exp(0) = 1
But |y| > 1, so no solution here.
Thus, the only critical point is at m = 1.
However, the problem states there are two discontinuities at m = a and m = b with a < b.
This suggests we might have missed another case.
Let's consider the transition point where |x| = 1.
At x = 1, f^{-1}(1) = 1(5 - 1)/2 = 2
So, f(2) = 1
The line y = m(x - 1) passes through (1,0).
At x = 2, y = m(2 - 1) = m
For the line to be tangent to f(x) at x = 2, f(2) = m and f'(2) = m.
f(2) = 1, so m = 1.
f'(2) = 1 / f^{-1}'(1) = 1 / ((5 - 3(1)^2)/2) = 2/2 = 1
So, m = 1 is indeed a critical point.
For the other critical point, consider the behavior as m increases.
For large m, the line y = m(x - 1) will intersect the exponential part of f(x) at one point.
The transition occurs when the line is tangent to the exponential part.
Let's solve for m where the line is tangent to f(x) for x > 1.
f(x) is the inverse of f^{-1}(y) = exp(y - 1) + 1 for y > 1.
So, f(x) = ln(x - 1) + 1 for x > 2 (since f^{-1}(1) = 2).
The line y = m(x - 1) must be tangent to y = ln(x - 1) + 1.
Set ln(x - 1) + 1 = m(x - 1)
And the derivative condition: 1/(x - 1) = m
Substitute m = 1/(x - 1) into the first equation:
ln(x - 1) + 1 = (x - 1)/(x - 1) = 1
So, ln(x - 1) = 0 => x - 1 = 1 => x = 2
But x = 2 is the transition point, not in the x > 2 region.
Thus, no other tangency points exist in the x > 2 region.
This suggests that the only discontinuity is at m = 1, but the problem states two discontinuities.
Perhaps the other discontinuity is at m = 0.
For m = 0, the line is y = 0.
The number of intersections with f(x) is the number of solutions to f(x) = 0.
For x <= 1, f(x) is the inverse of f^{-1}(y) = y(5 - y^2)/2.
Solve f(x) = 0 => x = f^{-1}(0) = 0.
For x > 1, f(x) = ln(x - 1) + 1 > 1 > 0.
So, only one intersection at x = 0.
For m slightly positive, the line y = m(x - 1) will intersect f(x) at two points (one for x < 1 and one for x > 1).
Thus, g(m) jumps from 1 to 2 at m = 0.
Therefore, the discontinuities are at m = 0 and m = 1.
Now, compute the required expression:
g(a) * lim_{m -> a+} g(m) + g(b) * (ln b / b)^2
Here, a = 0, b = 1.
g(0) = 1 (only one intersection at x = 0).
lim_{m -> 0+} g(m) = 2 (for m > 0, two intersections).
g(1) = 1 (tangency at x = 2).
(ln 1 / 1)^2 = 0.
So, the expression is:
1 * 2 + 1 * 0 = 2.
[/PYTHON]
[THOUGHT] The previous approach identified the discontinuities at ( m = 0 ) and ( m = 1 ).
- For ( m = 0 ), ( g(0) = 1 ) (only one intersection at ( x = 0 )).
- For ( m ) slightly greater than 0, ( g(m) = 2 ) (two intersections).
- For ( m = 1 ), ( g(1) = 1 ) (tangency at ( x = 2 )).
- The term ( \left( \frac{\ln 1}{1} \right)^2 = 0 ).
Thus, the expression evaluates to: [ g(0) \times \left(\lim_{m \to 0^+} g(m)\right) + g(1) \times \left( \frac{\ln 1}{1} \right)^2 = 1 \times 2 + 1 \times 0 = 2. ]
[/THOUGHT] \boxed{2}