Question

Find the exact values of cos (3pi/4radians) and sin (3pi/4 Radians)

Answer 1

$\cos\dfrac{3\pi}{4}=\cos\left(\pi-\dfrac{\pi}{4}\right)=-\cos\dfrac{\pi}{4}=-\dfrac{\sqrt2}{2}$

$\sin\dfrac{3\pi}{4}=\sin\left(\pi-\dfrac{\pi}{4}\right)=\sin\dfrac{\pi}{4}=\dfrac{\sqrt2}{3}$

Look at the picture.

$\dfrac{\pi}{2} < \dfrac{3\pi}{4} < \pi\\\\therefoere\\\\\cos\dfrac{3\pi}{4} < 0\ and\ \sin\dfrac{3\pi}{4} > 0$