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CIE 9709 2023 June Paper 32 Q1

A Level / CIE / P3

CIE 9709 2023 June Paper 32 Paper · Question 1

题目

Problem

Solve the inequality ∣5x−3∣<2∣3x−7∣|5x-3|<2|3x-7|.

(4)
题目中文翻译

解不等式 ∣5x−3∣<2∣3x−7∣|5x-3|<2|3x-7|。

(4)
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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两边都是非负数,可以等价平方。把二次式因式分解后,用开口方向确定外侧区间。

答题过程

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Both sides are non-negative, so squaring gives an equivalent inequality:

(5x−3)2<4(3x−7)2.(5x-3)^2<4(3x-7)^2.

Expanding and rearranging,

25x2−30x+9< 36x2−168x+196,11x2−138x+187> 0,(11x−17)(x−11)> 0.\begin{align*} 25x^2-30x+9<&\,36x^2-168x+196,\\[4mm] 11x^2-138x+187>&\,0,\\[4mm] (11x-17)(x-11)>&\,0. \end{align*}

The product is positive outside the two roots, so

x<1711orx>11.\boxed{x<\frac{17}{11}\quad\text{or}\quad x>11}.