Question

How to prove `sin^2(-pi/8)=sin^2((7pi)/8)` ?

Answer 1

`LHS=sin^2(-pi/8)`

`=(sin(-pi/8))^2`

`=(-sin(pi/8))^2`

`=sin^2(pi/8)`

`=sin^2(pi-pi/8)=sin^2((7pi)/8)=RHS`