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CIE 9709 2026 June Paper 31 Q1

A Level / CIE / P3

CIE 9709 2026 June Paper 31 Paper · Question 1

题目

Problem

Solve the inequality 3∣x+4∣>∣2x−1∣3|x+4|>|2x-1|.

(4)
题目中文翻译

解不等式 3∣x+4∣>∣2x−1∣3|x+4|>|2x-1|。

(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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两边都是非负量,可以等价地平方。把平方差分解,再根据两个一次因子的符号判断。

答题过程

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Squaring is equivalent because both sides are nonnegative. Thus

9(x+4)2>(2x−1)29(x+4)^2>(2x-1)^2

is equivalent to

(3x+12−2x+1)(3x+12+2x−1)>0,(3x+12-2x+1)(3x+12+2x-1)>0,

or (x+13)(5x+11)>0(x+13)(5x+11)>0. The two factors have the same sign outside their roots, giving x<−13x<-13 or x>−11/5x>-11/5.

解法二

思路

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也可以先根据 x+4x+4 的符号去掉左边绝对值。对正数 cc,∣b∣<c|b|<c 等价于 −c<b<c-c<b<c。

答题过程

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For x<−4x<-4, the inequality becomes ∣2x−1∣<−3x−12|2x-1|<-3x-12. This requires both

2x−1< −3x−12,−(2x−1)< −3x−12,\begin{align*} 2x-1<&\,-3x-12,\\[4mm] -(2x-1)<&\,-3x-12, \end{align*}

giving x<−11/5x<-11/5 and x<−13x<-13, hence x<−13x<-13.

At x=−4x=-4, the left side is zero and the inequality fails. For x>−4x>-4, it becomes ∣2x−1∣<3x+12|2x-1|<3x+12, requiring x>−13x>-13 and x>−11/5x>-11/5. Thus x>−11/5x>-11/5. Combining gives x<−13x<-13 or x>−11/5x>-11/5.