Question

Help with trig problem..

Find cos(s+t) and cos(s-t) if sin s = 2/3 and sin t = -1/3 s is in quadrant 1 and t is 3 quadrant.

I know I need this:
cos(s+t) = cos(s)*cos(t)-sin(s)*sin(t)
cos(s-t) = cos(s)*cos(t)+sin(s)*sin(t)

however im stuck on what do I plug in

thank you

Answer 1

based on the formula
sin= opposite divided by hypotunese
tan= opposite divided by adjacent
cos= adjacent divided by hypotunese

Answer 2

do apply above formula