Question

Prove the following :

cos90° = 1 – 2 sin²45° = 2cos²45° – 1

Answer 1

We know that

cos(90^o) = 0

taking LHS = cos 90° = 0

Now solving RHS 1- 2sin² 45°

= 1- 1

= 0

= RHS

Now, solving RHS = 2cos² 45° - 1 , we get

= 1- 1

= 0

Hence, proved.