cos(θ)=-((3)/(7)) where pi<theta <3pi/2 find value sin2 theta

Answer 1

1. Get the inverse of each side in cos(θ)=-((3)/(7)).

Cos^-1 (3/7) = theta.

2. From trig identities, we know sin2θ = 2sinθcosθ

Substitute that in for sin2θ and just solve since you figured out θ in part 1 and you were given what cosθ equals, which is 3/7.

Answer 2

Oh, I forgot to add the negative sign with 3/7.