Question

Question #d87b9

Answer 1

`LHS=Cos^2 (pi/8)+cos^2 ((3pi)/8)+cos^2 ((5pi)/8)+ cos^2 ((7pi)/8 )`

`=Cos^2( pi/8)+cos^2(pi/2-pi/8)+cos^2 ((5pi)/8)+ cos^2 ((3pi)/2-(5pi)/8 )`

`=Cos^2( pi/8)+(-sin(pi/8))^2+cos^2 ((5pi)/8)+ sin^2 ((5pi)/8 )`

`=Cos^2( pi/8)+sin^2(pi/8)+cos^2 ((5pi)/8)+ sin^2 ((5pi)/8 )`

`=1+1=2=RHS`

Proved