Originally Posted by
Jhevon well, you should pretty much know by heart that $\displaystyle \sin x = \cos x$ for $\displaystyle x = \frac {\pi}{4} + k \pi$
but if you wanted to work it out explicitly, here's what to do
$\displaystyle \sin x = \cos x$
$\displaystyle \Rightarrow \sin^2 x = \cos^2 x$
$\displaystyle \Rightarrow \cos^2 x - \sin^2 x = 0$
$\displaystyle \Rightarrow \cos 2x = 0$ ........you should also know for what values $\displaystyle \cos x = 0$
$\displaystyle \Rightarrow 2x = \frac {\pi}{2} + 2k \pi$
$\displaystyle \Rightarrow x = \frac {\pi}{4} + k \pi$
Now i leave the easy part for you. what are the values in the interval we were given?