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CIE 9709 2026 June Paper 12 Q5

A Level / CIE / P1

CIE 9709 2026 June Paper 12 Paper · Question 5

题目

Problem

The equation of a curve is such that d2ydx2=6x2+p\frac{\mathrm{d}^2y}{\mathrm{d}x^2}=6x^2+p, where pp is a constant. The curve has minimum points at (2,3)(2,3) and (−2,3)(-2,3).

Find the coordinates of the other stationary point of the curve.

(7)
题目中文翻译

一条曲线满足 d2ydx2=6x2+p\frac{\mathrm{d}^2y}{\mathrm{d}x^2}=6x^2+p,其中 pp 为常数。曲线在 (2,3)(2,3) 和 (−2,3)(-2,3) 处有极小值点。

求曲线上另一个驻点的坐标。

(7)
原卷通用作答要求

Answer all questions. You should use a calculator where appropriate.

You must show all necessary working clearly; no marks will be given for unsupported answers from a calculator.

Give non-exact numerical answers correct to 3 significant figures, or 1 decimal place for angles in degrees, unless a different level of accuracy is specified in the question.

请回答所有题目。适当时应使用计算器。必须清楚展示所有必要的计算过程;仅给出计算器答案而没有过程,不予评分。除非题目另有精度要求,非精确数值答案保留 3 位有效数字,以度为单位的角度保留 1 位小数。

解答

解法一

思路

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积分一次后,两个极小点的一阶导数都为零,正好确定 pp 与第一个常数。再积分并用已知高度求第二个常数。

答题过程

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Integrating gives y′=2x3+px+Cy'=2x^3+px+C. At x=2x=2 and x=−2x=-2, respectively,

16+2p+C=0,−16−2p+C=0.16+2p+C=0,\qquad -16-2p+C=0.

Adding gives C=0C=0, and then p=−8p=-8. Thus y′=2x(x−2)(x+2)y'=2x(x-2)(x+2), so the other stationary point is at x=0x=0.

Integrating again gives y=12x4−4x2+Dy=\frac12x^4-4x^2+D. Since y(2)=3y(2)=3, we have 3=8−16+D3=8-16+D, so D=11D=11. The other stationary point is (0,11)(0,11).