Question

Find cos(pi/4-pi/6)

Answer 1

\(\bf cos(a-b)=cos(a)cos(b)+sin(a)sin(b)\\ \quad \\ \quad \\

cos\left(\frac{\pi}{4}-\frac{\pi}{6}\right)=cos\left(\frac{\pi}{4}\right)cos\left(\frac{\pi}{6}\right)+sin\left(\frac{\pi}{4}\right)sin\left(\frac{\pi}{6}\right)\)

and those are well known angles, so they'd be in your Unit Circle
recall the trig sum identities -> http://www.mathwords.com/s/sum_difference_identities.htm