How can you rearrange this formula to correctly find cosθ?

Answer 1

1) square both sides
sin^2(T/2) = (1 - cos(t))/2
2) multiply both sides by 2
2sin^2(t/2) = 1 - cos(t)
3) subtract 1 from both sides
2 sin^2(t/2) - 1 = -cos(t)
4) multiply both sides by -1
1 - 2sin^2(t/2) = cos(t)

It is the penultimate choice