Find sin2x, cos2x, and tan2x if cosx=−2/sqrt 5 and x terminates in quadrant II.
cosx = -2/√5 in QII, so
x = -2
y = 1
r = √5
so
sinx = 1/√5
tanx = -y/x = -1/2
Now just use the double-angle fornmulas to get the functions of 2x
x = -2
y = 1
r = √5
so
sinx = 1/√5
tanx = -y/x = -1/2
Now just use the double-angle fornmulas to get the functions of 2x