posted by Joe .
Given that SIN Theta = -1/sqrt(10) and theta is in quadrant 4, find sin2theta and cos2theta.
I'm not sure how to properly square the -1/sqrt10 and keep an exact answer other than decimal. Otherwise, my final answer is 1.632455533
if sintheta=-1/sqrt10, then
costheta= (10-1)/sqrt10= sqrt (9/10)
Then sin2theta= sintheta*costheta=-2/sqrt10*sqrt9/10
= sqrt9 /5=3/5=.6
check all that. I have no idea what you did.