Find all solutions on the interval 0 is less than or equal to x is less than 2π:
cos²x-cos(2x)=0
Hi nystudent2729,
We have $\displaystyle \cos^2(x)-\cos(2x)=0$ Note that $\displaystyle cos(2x) \equiv 2\cos^2(x)-1$ Thus we are left with
$\displaystyle \cos^2(x)-(2\cos^2(x)-1)=1-\cos^2(x)=0$
$\displaystyle \implies \cos^2(x)=1 \implies \cos(x)=\pm1$
Can you continue?