Question

given that sin theta equals 1/5 and that the terminal side is in quadrant 1, find exact answers for cos(theta+pi/4)

Answer 1

well if you draw a diagram



don't you need to find x using pythagoras' theorem....

and subsequently

\[\cos(\theta)\]

then use the expansion

\[\cos(\theta + \frac{\pi}{4}) = \cos(\theta)\cos(\frac{\pi}{4}) - \sin(\theta)\sin(\frac{\pi}{4})\]

hope it helps