Problem Analysis #10

Claude Opus 4.8 · Run 1

Correct
9.22s
1,124 toks

API · no tools. This is the prompt and response recorded for this attempt; a full solution may not have been returned.

Problem Statement

Return a single integer only. The problem has been revised so that no final answer is an irrational number, a parameterized expression, a range, a proof, a drawing, a graph, a locus equation, or a region description.

Let a>0a>0, and consider the parabola y=x2y=x^2. Starting from P(a,a2)P(a,a^2), let QPQ\ne P be the other intersection of the normal line to the parabola at PP with the parabola. Let RQR\ne Q be the other intersection of the normal line at QQ with the parabola.

If the minimum possible xx-coordinate of RR is MM, write M2=p/qM^2=p/q in lowest terms and find p+qp+q.

Ground Truth
33
Recorded model response / solution
Reasoning Process
<think> Parabola y=x². At point P(a,a²), slope of tangent is 2a, normal slope is -1/(2a).

Normal at P: y - a² = -1/(2a)(x - a).

Find other intersection Q with parabola. Let Q have x-coordinate b. For a chord that is normal at P: the normal line intersects parabola at x=a and x=b.

Line through (a,a²) and (b,b²) has slope (b²-a²)/(b-a) = a+b. This must equal normal slope -1/(2a). So a+b = -1/(2a), thus b = -a - 1/(2a).

Similarly normal at Q gives R with x-coordinate c: b + c = -1/(2b), so c = -b - 1/(2b).

We want minimize x-coordinate of R = c over a>0.

b = -a - 1/(2a). Since a>0, b is negative.

c = -b - 1/(2b).

Let me compute c as function of a. Let b = -(a + 1/(2a)). Note b<0.

c = -b - 1/(2b).

Let me set b negative. Let t = -b = a + 1/(2a) > 0.

Then c = t - 1/(2b) = t - 1/(2(-t)) = t + 1/(2t).

So c = t + 1/(2t) where t = a + 1/(2a).

We want minimum of c over a>0. c = t + 1/(2t), with t ranging over values of a+1/(2a) for a>0.

a + 1/(2a) has minimum at a = 1/√2: value = 1/√2 + 1/(2/√2)= 1/√2 + (√2)/2 = 1/√2+1/√2 = 2/√2 = √2. So t ≥ √2.

Now c(t) = t + 1/(2t) for t ≥ √2. This is increasing for t > 1/√2 (since derivative 1 - 1/(2t²) >0 when t²>1/2). So minimum at t=√2.

c = √2 + 1/(2√2) = √2 + 1/(2√2) = √2 + √2/4 = (4√2+√2)/4 = 5√2/4.

So M = 5√2/4. M² = 25·2/16 = 50/16 = 25/8.

p/q = 25/8, lowest terms, p+q = 33. </think>

\boxed{33}

Final Model Output
33

Comparative Analysis (P10) (Average across runs)

Averages use reported measurements only. Missing usage is not treated as zero.

Avg Time Taken

K-EXAONE-236B-A23B
77.5
DeepSeek V4 Pro
55.9
Solar Pro 3
41.5
Gemini 3.5 Flash
13.5
GPT-5.5
11.2
Claude Opus 4.8
9.0
KT Mi:dm 2.0 Base Instruct
3.3

Avg Token Usage

K-EXAONE-236B-A23B
11966.0
Solar Pro 3
6444.7
DeepSeek V4 Pro
3794.7
Gemini 3.5 Flash
3138.3
KT Mi:dm 2.0 Base Instruct
1946.7
Claude Opus 4.8
1157.7
GPT-5.5
811.0
    Tokyo · Problem 10 · Claude Opus 4.8 | EntropyMath