Posted by Joe on .
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

PreCalculus 
bobpursley,
if sintheta=1/sqrt10, then
costheta= (101)/sqrt10= sqrt (9/10)
check those.
Then sin2theta= sintheta*costheta=2/sqrt10*sqrt9/10
= sqrt9 /5=3/5=.6
cos2Theta=12sin^2 theta=12(1/10)=.8
check all that. I have no idea what you did.