How can you rearrange this formula to correctly find cosθ?

Question

Answer 1

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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