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CIE 9709 2022 June Paper 31 Q1

A Level / CIE / P3

CIE 9709 2022 June Paper 31 Paper · Question 1

题目

Problem

Solve the equation 2(32x−1)=4x+12(3^{2x-1})=4^{x+1}, giving your answer correct to 2 decimal places.

(4)
题目中文翻译

解方程 2(32x−1)=4x+12(3^{2x-1})=4^{x+1},答案精确到小数点后 2 位。

(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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直接取对数,用幂的对数法则把指数变成乘数,再解一次方程。

答题过程

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Taking natural logarithms,

ln⁡2+(2x−1)ln⁡3=(x+1)ln⁡4.\ln2+(2x-1)\ln3=(x+1)\ln4.

Thus

x(2ln⁡3−ln⁡4)=ln⁡4+ln⁡3−ln⁡2=ln⁡6.x(2\ln3-\ln4)=\ln4+\ln3-\ln2=\ln6.

Hence

x=ln⁡6ln⁡(9/4)=2.209511….x=\frac{\ln6}{\ln(9/4)}=2.209511\ldots.

Therefore x=2.21\boxed{x=2.21} to 2 decimal places.

解法二

思路

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先用指数法则合并含 xx 的项,化成一个指数方程再取对数。

答题过程

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Rearranging with the laws of indices,

23 9x= 4 4x,(94)x= 6.\begin{align*} \frac23\,9^x=&\,4\,4^x,\\[4mm] \bigg(\frac94\bigg)^x=&\,6. \end{align*}

Taking logarithms,

xln⁡94=ln⁡6.x\ln\frac94=\ln6.

Therefore

x=ln⁡6ln⁡(9/4)≈2.21x=\frac{\ln6}{\ln(9/4)}\approx\boxed{2.21}

to 2 decimal places.