Question

Which of the following is a double angle identity?sinθ=cos(π2−θ)sine theta is equal to cosine of open paren pi over 2 minus theta close parencos(2θ)=cos2θ−sin2θcosine of 2 theta is equal to cosine squared theta minus sine squared thetasin(−θ)=−sinθsine of negative theta is equal to negative sine thetacos2θ+sin2θ=1

Answer 1

The double angle formulas are

sin (2 theta) = 2 sin theta cos theta

cos (2 theta) = cos ^2 theta - sin ^2 theta

= 2 cos ^2 theta - 1

= 1 - 2 sin ^2 theta

tan ( 2 theta) = 2 tan thets / ( 1 - tan ^2 theta)

We have cos (2 theta) = cos ^2 theta - sin ^2 theta