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CIE 9709 2025 June Paper 11 Q6

A Level / CIE / P1

CIE 9709 2025 June Paper 11 Paper · Question 6

题目

Problem

The equation of a curve is 2x2−kxy+2=02x^2 - kxy + 2 = 0 and the equation of a line is y=px+3y = px + 3, where kk and pp are constants.

(a) Given that k=2k = 2 and p=11p = 11, find the coordinates of the points of intersection of the curve and the line.

[4]

(b) Given instead that p=4p = 4, find the set of values of kk for which the curve and the line do not intersect.

[5]
题目中文翻译

一条曲线的方程为 2x2−kxy+2=02x^2 - kxy + 2 = 0,一条直线的方程为 y=px+3y = px + 3,其中 kk 和 pp 为常数。

(a) 已知 k=2k = 2、p=11p = 11,求曲线与直线交点的坐标。

[4]

(b) 改为已知 p=4p = 4,求使曲线与直线不相交的 kk 的取值范围。

[5]

解答

(a)

解法一

思路

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把直线的 yy 表达式代入曲线方程。先求交点的横坐标,再用直线求纵坐标。

答题过程

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Here y=11x+3y=11x+3, so

2x2−2x(11x+3)+2=0⟹10x2+3x−1=(5x−1)(2x+1)=0.2x^2-2x(11x+3)+2=0 \quad\Longrightarrow\quad 10x^2+3x-1=(5x-1)(2x+1)=0.

The roots are x=15x=\frac15 and x=−12x=-\frac12. Substitution into the line gives the intersections (15,265)(\frac15,\frac{26}5) and (−12,−52)(-\frac12,-\frac52).

(b)

解法一

思路

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代入直线后,若二次方程没有实根就没有交点。另检查二次项系数为零时的退化情形。

答题过程

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With y=4x+3y=4x+3, intersections correspond to

(2−4k)x2−3kx+2=0.(2-4k)x^2-3kx+2=0.

If k=12k=\frac12, this becomes −32x+2=0-\frac32x+2=0, which has a solution. For k≠12k\ne\frac12, there are no real roots precisely when the discriminant is negative:

(−3k)2−4(2−4k)(2)=9k2+32k−16=(k+4)(9k−4)<0.(-3k)^2-4(2-4k)(2) =9k^2+32k-16=(k+4)(9k-4)<0.

Thus −4<k<49-4<k<\frac49, which already excludes k=12k=\frac12.