Problem Analysis #20

64.23s
6,115 toks
Problem Statement

Let a function f(x)f(x) defined on the set of all real numbers satisfyf(x)=xsin(πx)for x[0,2],f(x) = x \sin(\pi x) \qquad \text{for } x \in [0,2],andf(x)=2f(x2)for all real x.f(x) = 2 f(x-2) \qquad \text{for all real } x.Consider the region enclosed by the curve y=f(x)y = f(x), the line y=21012(x2026),y = 2^{1012}(x - 2026),and the two vertical lines x=2026x = 2026 and x=2027x = 2027.The area of this region is equal to21012(p+qπ+r3π),2^{1012}\left(p + \frac{q}{\pi} + \frac{r\sqrt{3}}{\pi}\right),for some rational numbers p,q,rp, q, r.Find the value of 2028 $$\cdot$$ p $$\cdot$$ q $$\cdot$$ r.oindent

Ground Truth
1352
Execution Trace
Reasoning Process

[THOUGHT] We need to understand the problem fully. There's a piecewise-defined function f(x):

  • For x in [0,2], f(x) = x sin(πx).
  • For all real x, f(x) = 2 f(x-2).

This is a functional equation that defines f recursively. Let's interpret: For any x, we can subtract multiples of 2 to bring it into [0,2], but each time we subtract 2, we multiply the function value by 2.

Specifically, for any integer n such that x - 2n ∈ [0,2], we have f(x) = 2^n f(x - 2n). But careful: The equation f(x) = 2 f(x-2) holds for all real x. That means f(x) = 2 f(x-2). Applying repeatedly: f(x) = 2^k f(x - 2k) for any integer k. So if we choose k such that x - 2k ∈ [0,2], then f(x) = 2^k f(x - 2k).

Now we consider region enclosed by curve y = f(x), line y = 2^{1012}(x - 2026), vertical lines x = 2026 and x = 2027. So region is between these two curves from x=2026 to x=2027.

We need area of that region. Area = ∫_{2026}^{2027} |f(x) - 2^{1012}(x - 2026)| dx? Actually region enclosed by those four curves: likely the region bounded above/below by them. Since both curves are defined, we need the absolute difference between them integrated.

But we need to know which is above which. Let's compute f(x) on [2026,2027]. Since 2026 is even? 2026/2 = 1013, so 2026 = 21013. So x in [2026,2027] corresponds to subtracting 21013 = 2026? Wait, we need to bring x into [0,2] by subtracting multiples of 2.

Let x = 2026 + t, where t ∈ [0,1]. Then x - 2*1013 = 2026 + t - 2026 = t ∈ [0,1] which is subset of [0,2]. So k = 1013. Then f(x) = 2^{1013} f(t) = 2^{1013} * t sin(π t) (since t ∈ [0,1] ⊂ [0,2] and sin(π t) is sin(π t)).

Thus f(x) = 2^{1013} * t sin(π t) where t = x - 2026.

Now the line is y = 2^{1012} (x - 2026) = 2^{1012} t.

So we have f(x) = 2^{1013} t sin(π t) and line L(x) = 2^{1012} t.

Factor 2^{1012}: f(x) = 2^{1012} * 2 * t sin(π t) = 2^{1012} * 2 t sin(π t).

Thus difference: f(x) - L(x) = 2^{1012} t (2 sin(π t) - 1).

Now we need area between curves from t=0 to t=1. But which curve is above? Let's check sign: For t in [0,1], sin(π t) ≥ 0, so 2 sin(π t) ≥ 0. But 2 sin(π t) - 1 could be positive or negative depending on t.

Find where 2 sin(π t) - 1 = 0 → sin(π t) = 1/2 → π t = π/6 or 5π/6 within [0,π] (since t∈[0,1], πt∈[0,π]). So t = 1/6 or t = 5/6.

Thus for t ∈ [0,1/6), sin(π t) < 1/2 → 2 sin(π t) - 1 < 0 → f(x) < L(x). For t ∈ (1/6,5/6), sin(π t) > 1/2 → f(x) > L(x). For t ∈ (5/6,1], sin(π t) < 1/2 → f(x) < L(x).

Thus the region enclosed by the two curves and vertical lines x=2026 and x=2027 is the region between them, but we need to compute area as the integral of absolute difference. So area = ∫_{t=0}^{1} |2^{1012} t (2 sin(π t) - 1)| dt = 2^{1012} ∫_0^1 t |2 sin(π t) - 1| dt.

Given answer format: area = 2^{1012} (p + q/π + r√3/π). So we need to compute I = ∫_0^1 t |2 sin(π t) - 1| dt, express as p + q/π + r√3/π, where p,q,r rational.

Then area = 2^{1012} * I.

Finally, we need 2028 * p * q * r.

We need to compute I exactly.

Let’s compute I = ∫_0^1 t |2 sin(π t) - 1| dt.

Split intervals: [0,1/6], [1/6,5/6], [5/6,1].

Define g(t) = 2 sin(π t) - 1.

On [0,1/6], g(t) ≤ 0, so |g(t)| = -g(t) = 1 - 2 sin(π t). On [1/6,5/6], g(t) ≥ 0, so |g(t)| = g(t) = 2 sin(π t) - 1. On [5/6,1], g(t) ≤ 0, so |g(t)| = -g(t) = 1 - 2 sin(π t).

Thus I = ∫0^{1/6} t (1 - 2 sin(π t)) dt + ∫{1/6}^{5/6} t (2 sin(π t) - 1) dt + ∫_{5/6}^{1} t (1 - 2 sin(π t)) dt.

We can compute each integral analytically using integration by parts or symbolic integration.

Let’s compute using Python with sympy to get exact expression.

We'll compute I = ∫_0^1 t |2 sin(π t) - 1| dt.

We'll compute each piece and sum.

Let’s write Python code.

[PYTHON] import sympy as sp

t = sp.symbols('t', real=True)

Define integrand piecewise

f1 = t * (1 - 2sp.sin(sp.pit)) # 0 to 1/6 f2 = t * (2sp.sin(sp.pit) - 1) # 1/6 to 5/6 f3 = t * (1 - 2sp.sin(sp.pit)) # 5/6 to 1

Integrate

I1 = sp.integrate(f1, (t, 0, sp.Rational(1,6))) I2 = sp.integrate(f2, (t, sp.Rational(1,6), sp.Rational(5,6))) I3 = sp.integrate(f3, (t, sp.Rational(5,6), 1))

I = sp.simplify(I1 + I2 + I3) I [/PYTHON]

But careful: sp.integrate may give expression with π and sqrt(3). Let's run.

We'll also compute numeric to check.

Let's execute. </think>

[PYTHON] import sympy as sp

t = sp.symbols('t', real=True)

Define integrand piecewise

f1 = t * (1 - 2sp.sin(sp.pit)) # 0 to 1/6 f2 = t * (2sp.sin(sp.pit) - 1) # 1/6 to 5/6 f3 = t * (1 - 2sp.sin(sp.pit)) # 5/6 to 1

Integrate

I1 = sp.integrate(f1, (t, 0, sp.Rational(1,6))) I2 = sp.integrate(f2, (t, sp.Rational(1,6), sp.Rational(5,6))) I3 = sp.integrate(f3, (t, sp.Rational(5,6), 1))

I = sp.simplify(I1 + I2 + I3) I [/PYTHON]

Tool Output
[PYTHON OUTPUT] (-12 - pi + 12*sqrt(3))/(6*pi) [/PYTHON OUTPUT] [PYTHON OUTPUT] (-12 - pi + 12*sqrt(3))/(6*pi) [/PYTHON OUTPUT]
Reasoning Process

[THOUGHT] The Python output gives the value of the integral as ((-12 - \pi + 12\sqrt{3})/(6\pi)). This is the area of one period of the function's envelope relative to the line (y = t)? Wait, the problem's region is between (y = f(x)) and (y = 2^{1012}(x - 2026)) from (x = 2026) to (2027). But (f) is periodic with period 2 and scaled by (2^{1012}) horizontally? Actually (f(x) = 2 f(x-2)) means (f(x+2) = f(x)/2)? Let's check: (f(x) = 2 f(x-2)) implies (f(x+2) = f(x)/2)? No: replace (x) by (x+2): (f(x+2) = 2 f(x)). So it's doubling when shifting right by 2. That means (f(x+2) = 2 f(x)). So over each period of length 2, the function is scaled by factor 2. But the problem says (f(x) = 2 f(x-2)) for all real (x). That means (f(x+2) = 2 f(x)). So (f) grows by factor 2 every 2 units.

Given (f(x) = x \sin(\pi x)) on ([0,2]), we can shift to other intervals: For (x \in [2,4]), (f(x) = 2 f(x-2) = 2 (x-2) \sin(\pi (x-2))). But (\sin(\pi(x-2)) = \sin(\pi x - 2\pi) = \sin(\pi x)). So (f(x) = 2 (x-2) \sin(\pi x)) for (x \in [2,4]). Similarly, for (x \in [2026, 2028]), (f(x) = 2^{1013} (x - 2026) \sin(\pi x))? Let's derive: For (x \in [2,4]), (f(x) = 2 f(x-2) = 2 (x-2) \sin(\pi (x-2)) = 2 (x-2) \sin(\pi x)). For (x \in [4,6]), (f(x) = 2 f(x-2) = 2 \cdot [2 (x-4) \sin(\pi x)] = 4 (x-4) \sin(\pi x)). So in general, for (x \in [2k, 2k+2]), (f(x) = 2^k (x - 2k) \sin(\pi x)). Here (2026 = 2 \cdot 1013), so (k = 1013). Then (f(x) = 2^{1013} (x - 2026) \sin(\pi x)) for (x \in [2026, 2028]). The region is between (y = f(x)) and (y = 2^{1012}(x - 2026)) from (x = 2026) to (2027).

Thus the difference is (f(x) - 2^{1012}(x - 2026) = [2^{1013}(x - 2026) \sin(\pi x) - 2^{1012}(x - 2026)] = 2^{1012}(x - 2026)[2 \sin(\pi x) - 1]).

We need the area between these curves from (x = 2026) to (2027). That's (\int_{2026}^{2027} |2^{1012}(x - 2026)[2 \sin(\pi x) - 1]| , dx). But sign changes? Let (t = x - 2026), then (t \in [0,1]), and (\sin(\pi x) = \sin(\pi(t + 2026)) = \sin(\pi t + 2026\pi)). Since (2026) is even, (2026\pi) is multiple of (2\pi), so (\sin(\pi t + 2026\pi) = \sin(\pi t)). So the integrand becomes (2^{1012} t [2 \sin(\pi t) - 1]).

The area between the curves is (\int_0^1 |2^{1012} t (2 \sin(\pi t) - 1)| dt = 2^{1012} \int_0^1 |t (2 \sin(\pi t) - 1)| dt).

The earlier Python computed (\int_0^1 |t (1 - 2 \sin(\pi t))| dt)? Wait, they defined f1 = t*(1 - 2sin(pit)) for 0 to 1/6, f2 = t*(2sin(pit) - 1) for 1/6 to 5/6, f3 = t*(1 - 2sin(pit)) for 5/6 to 1. That matches (|t (2\sin(\pi t) - 1)|) because:

For (t \in [0,1/6]), (2\sin(\pi t) - 1 \le 0)? Let's check: at (t=0), (2\sin 0 - 1 = -1 < 0). At (t=1/6), (2\sin(\pi/6) - 1 = 2*(1/2) - 1 = 0). So on ([0,1/6]), (2\sin(\pi t) - 1 \le 0), so (|t (2\sin(\pi t) - 1)| = t(1 - 2\sin(\pi t))). That's f1.

For (t \in [1/6, 5/6]), (2\sin(\pi t) - 1 \ge 0)? At (t=1/2), (2\sin(\pi/2) - 1 = 2 - 1 = 1 > 0). At (t=5/6), (2\sin(5\pi/6) - 1 = 2*(1/2) - 1 = 0). So (2\sin(\pi t) - 1 \ge 0) on ([1/6, 5/6]), so (|t (2\sin(\pi t) - 1)| = t(2\sin(\pi t) - 1)). That's f2.

For (t \in [5/6, 1]), (2\sin(\pi t) - 1 \le 0)? At (t=1), (2\sin(\pi) - 1 = -1 < 0). So (|t (2\sin(\pi t) - 1)| = t(1 - 2\sin(\pi t))). That's f3.

Thus the Python computed exactly (A = \int_0^1 |t (2\sin(\pi t) - 1)| dt = (-12 - \pi + 12\sqrt{3})/(6\pi)).

Thus the area of the region is (2^{1012} \cdot A = 2^{1012} \cdot \frac{-12 - \pi + 12\sqrt{3}}{6\pi}).

The problem says this area equals (2^{1012} \left(p + \frac{q}{\pi} + \frac{r\sqrt{3}}{\pi}\right)).

So equate: (\frac{-12 - \pi + 12\sqrt{3}}{6\pi} = p + \frac{q}{\pi} + \frac{r\sqrt{3}}{\pi}).

Multiply by 1: (p + \frac{q}{\pi} + \frac{r\sqrt{3}}{\pi} = \frac{-12}{6\pi} - \frac{\pi}{6\pi} + \frac{12\sqrt{3}}{6\pi} = \frac{-2}{\pi} - \frac{1}{6} + \frac{2\sqrt{3}}{\pi}).

Thus (p = -1/6), (q/\pi = -2/\pi \Rightarrow q = -2), (r\sqrt{3}/\pi = 2\sqrt{3}/\pi \Rightarrow r = 2).

So (p = -1/6), (q = -2), (r = 2).

Then (2028 \cdot p \cdot q \cdot r = 2028 \cdot (-1/6) \cdot (-2) \cdot 2).

Compute: ((-1/6) \cdot (-2) = 1/3). Then ((1/3) \cdot 2 = 2/3). Then (2028 \cdot (2/3) = 2028/3 \cdot 2 = 676 \cdot 2 = 1352).

Thus final answer is 1352.

\boxed{1352}

Final Model Output
1352

Comparative Analysis (P20) (Average across runs)

Avg Time Taken

K-EXAONE-236B-A23B
1117.7
Solar-Open-100B
743.0
Solar-Pro-2 (31B)(high)
209.1
Llama-VARCO-8B-Instruct
194.6
Gemini-3-Pro-Preview
117.1
A.X-4.0 (72B)
98.1
Grok-4.1-fast
91.6
Kanana-2-30B-Thinking
82.5
HCX-007(high)
65.9
K-EXAONE-236B-A23B
64.2
GPT-5.1 (high)
59.3
Deepseek-V3.2
40.9
Kanana-2-30B-Thinking-2601
39.3
Claude-Opus-4.5
27.1
GPT-5.2 (high)
22.2
axk1
8.3
EXAONE-4.0.1-32B (high)
7.6

Avg Token Usage

K-EXAONE-236B-A23B
231341.3
Solar-Open-100B
23307.0
Kanana-2-30B-Thinking
15652.0
Grok-4.1-fast
15328.0
Gemini-3-Pro-Preview
13814.0
Solar-Pro-2 (31B)(high)
12507.0
Kanana-2-30B-Thinking-2601
9179.5
HCX-007(high)
7833.0
GPT-5.1 (high)
7486.0
Deepseek-V3.2
7264.0
Llama-VARCO-8B-Instruct
7065.0
K-EXAONE-236B-A23B
6115.0
GPT-5.2 (high)
5568.0
Claude-Opus-4.5
5400.0
EXAONE-4.0.1-32B (high)
5036.0
axk1
3092.0
A.X-4.0 (72B)
3005.0