Problem Analysis #31

21.94s
5,686 toks
Problem Statement

For all real numbers xx with 2x2-2 \leq x \leq 2, the inequalityk2x3+3x212x8k-k \leq 2x^3 + 3x^2 - 12x - 8 \leq kholds. Find the smallest possible positive value of kk. [3 points]\

Ground Truth
15
Execution Trace
Reasoning Process

[THOUGHT] The function (f(x) = 2x^3 + 3x^2 - 12x - 8) must satisfy (-k \leq f(x) \leq k) for all (x \in [-2, 2]). This requires (k) to be at least the maximum of (|f(x)|) over the interval.

First, find the critical points by setting the derivative (f'(x) = 6x^2 + 6x - 12 = 0). Solving (x^2 + x - 2 = 0) gives (x = -2) and (x = 1). These are within ([-2, 2]), along with the endpoints.

Evaluate (f(x)) at (x = -2), (x = 1), and (x = 2):

  • (f(-2) = 2(-8) + 3(4) - 12(-2) - 8 = -16 + 12 + 24 - 8 = 12)
  • (f(1) = 2(1) + 3(1) - 12(1) - 8 = 2 + 3 - 12 - 8 = -15)
  • (f(2) = 2(8) + 3(4) - 12(2) - 8 = 16 + 12 - 24 - 8 = -4)

The absolute values are:

  • (|f(-2)| = 12)
  • (|f(1)| = 15)
  • (|f(2)| = 4)

The maximum absolute value is 15, so (k \geq 15). Testing other points in ([-2, 2]) (e.g., (x = 0), (x = -1), (x = 1.5)) yields values less than 15 in absolute value. Thus, the smallest (k) is 15.

\boxed{15}

Reasoning Process

[THOUGHT] I will use the Python tool to compute the function values at the critical points and endpoints to find the maximum absolute value. [/THOUGHT] [PYTHON]

Define the function

def f(x): return 2x**3 + 3x**2 - 12*x - 8

Evaluate at critical points and endpoints

points = [-2, 1, 2] values = [f(p) for p in points] abs_values = [abs(v) for v in values] max_abs = max(abs_values) print(max_abs) [/PYTHON]

Tool Output
[PYTHON OUTPUT] 15 [/PYTHON OUTPUT]
Reasoning Process

\boxed{15}

Final Model Output
15

Comparative Analysis (P31) (Average across runs)

Avg Time Taken

EXAONE-4.0.1-32B (high)
2301.7
Solar-Open-100B
640.8
K-EXAONE-236B-A23B
189.6
Gemini-3-Pro-Preview
170.7
Llama-VARCO-8B-Instruct
98.0
Deepseek-V3.2
67.5
HCX-007(high)
54.8
Solar-Pro-2 (31B)(high)
35.0
Kanana-2-30B-Thinking
33.8
Kanana-2-30B-Thinking-2601
21.2
A.X-4.0 (72B)
15.2
GPT-5.2 (high)
14.8
GPT-5.1 (high)
13.3
Claude-Opus-4.5
12.6
K-EXAONE-236B-A23B
12.4
Grok-4.1-fast
10.0
axk1
4.4

Avg Token Usage

EXAONE-4.0.1-32B (high)
37496.0
K-EXAONE-236B-A23B
27042.0
Kanana-2-30B-Thinking
7460.0
Solar-Pro-2 (31B)(high)
7096.0
HCX-007(high)
5642.0
Kanana-2-30B-Thinking-2601
5493.5
Solar-Open-100B
5057.0
Llama-VARCO-8B-Instruct
4580.0
GPT-5.2 (high)
4360.0
Gemini-3-Pro-Preview
4189.0
K-EXAONE-236B-A23B
4115.0
Grok-4.1-fast
3931.0
Deepseek-V3.2
3561.0
Claude-Opus-4.5
3451.0
A.X-4.0 (72B)
3174.0
GPT-5.1 (high)
3116.0
axk1
2308.0