1. trig

can someone help me here? i know these are simple but i can't get it. Find sin(x/2) when cos(x)=3/7. and find cos(x/2) when sin(x)=5/12

2. Originally Posted by jarny
can someone help me here? i know these are simple but i can't get it. Find sin(x/2) when cos(x)=3/7. and find cos(x/2) when sin(x)=5/12
use the half-angle formulas:

$\sin \frac x2 = \pm \sqrt{\frac {1 - \cos x}2}$

and

$\cos \frac x2 = \pm \sqrt{\frac {1 + \cos x}2}$

also, $\sin^2 x + \cos^2 x = 1$ will come in handy for the second one