Maths Olympiad Prep

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Algebra Difficulty 5.1 AIME, harder Find the answer

Example 1. Solve the equation
sin(x+π6)+cos(x+π6)=0 \sin \left(x+\frac{\pi}{6}\right)+\cos \left(x+\frac{\pi}{6}\right)=0 \text {. }

A number or a short expression. Fractions can be typed as 3/2, and spacing doesn't matter.

Solution

Solve cos(x+π6)=sin(x+π6π2)-\cos \left(x+\frac{\pi}{6}\right)=\sin \left(x+\frac{\pi}{6}-\frac{\pi}{2}\right)
=sin(xπ3), =\sin \left(x-\frac{\pi}{3}\right),

The original equation can be transformed into
sin(x+π6)=sin(xπ3).x+π6=nπ+(1)(xπ3). \begin{array}{l} \sin \left(x+\frac{\pi}{6}\right)=\sin \left(x-\frac{\pi}{3}\right) . \\ \therefore x+\frac{\pi}{6}=n \pi+(-1) \cdot\left(x-\frac{\pi}{3}\right) . \end{array}

When B=2k(kZ)\mathrm{B}=2 \mathrm{k}(\mathrm{k} \in \mathrm{Z}), the equation becomes
x+π6=2kπ+xπ3, no solution.  x+\frac{\pi}{6}=2 k \pi+x-\frac{\pi}{3} \text {, no solution. }

When n=2k+1(kZ)n=2 k+1 \quad(k \in Z), the equation becomes
x+π6=(2k+1)πx+π3,x=kπ+712π. \begin{array}{c} x+\frac{\pi}{6}=(2 \mathrm{k}+1) \pi-x+\frac{\pi}{3}, \\ \mathbf{x}=\mathrm{k} \pi+\frac{7}{12} \pi . \end{array}

The solution set of the original equation is {x:x=kπ+712π,kZ}\left\{\mathbf{x}: \mathbf{x}=\mathrm{k} \pi+\frac{7}{12} \pi, \mathrm{k} \in \mathrm{Z}\right\}.

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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.