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Algebra Difficulty 3.4 AMC 10/12 Find the answer

Translate the graph of y=2sin(2x+π3)y= \sqrt{2}\sin(2x+ \frac{\pi}{3}) to the right by φ\varphi (0<φ<π0<\varphi<\pi) units to obtain the graph of the function y=2sinx(sinxcosx)1y=2\sin x(\sin x-\cos x)-1. Find the value of φ\varphi.

A number or a short expression. Spacing and $ signs are ignored.

Solution

To translate the graph of y=2sin(2x+π3)y= \sqrt{2}\sin(2x+ \frac{\pi}{3}) to the right by φ\varphi (0<φ<π0<\varphi<\pi) units, we get the graph of y=2sin(2x2φ+π3)y= \sqrt{2}\sin(2x-2\varphi+ \frac{\pi}{3}).
According to the problem, we have y=2sinx(sinxcosx)1=2sin2xsin2x1=sin2xcos2x=2sin(2x+π4)=2sin(2x+5π4)y=2\sin x(\sin x-\cos x)-1=2\sin^2x-\sin 2x-1=-\sin 2x-\cos 2x=- \sqrt{2}\sin(2x+ \frac{\pi}{4})= \sqrt{2}\sin(2x+ \frac{5\pi}{4}).
Therefore, 2φ+π3=5π4+2kπ-2\varphi+ \frac{\pi}{3}= \frac{5\pi}{4}+2k\pi, where kZk\in \mathbb{Z}. This implies φ=kπ11π24\varphi=-k\pi- \frac{11\pi}{24}. Thus, φ=13π24\varphi= \boxed{\frac{13\pi}{24}}.
This problem involves using the transformation rules of the graph of the function y=Asin(ωx+φ)y=A\sin(\omega x+\varphi) and deriving formulas from these rules.
The main focus of this problem is on the application of the transformation rules and formula derivation for the function y=Asin(ωx+φ)y=A\sin(\omega x+\varphi), which is considered a basic problem.

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Source: NuminaMath-1.5, licensed Apache-2.0. Statement and solution reproduced as published; topic and difficulty added by this site.