Posted by steve on .
can you help me find cos 2x if sin x = 12/13 (x in 3rd quadrant)

trig 
Henry,
GIVEN: SinX = 12 / 13
SinX = 12/13 = 0.9231, X=67.38(1st.quad.), X = 67.38 + 180 = 247.38
( 3rd. quad, ), Z
2X = 2*247.34 = 494.76
COS2X = COS 494.76 = 0.7041