Find sin2x, cos2x, and tan2x if cosx= -1/sqrt5 and x terminates in quadrant 3

Question

Find sin2x, cos2x, and tan2x if cosx= -1/sqrt5 and x terminates in quadrant 3.

The answer i got was wrong and i'm not too sure on how to do it.

Answer 1

cosx = -1/sqr5

sinx = -2/sqr5

sin2x=2sinxcosx= 4/5=.8

cos2x=2cos^2(x)-1=-3/5=-.6

tanx =2

tan2x=sin2x/cos2x =2tanx/(1-tan^2(x))=-4/3=-1.333...

x =360- 116.565 =about 243.435 degrees in QIII

2x = 486.870 degrees in QII