Question

2*sqrt2cos^2(9p/8)-sqrt2

Answer 1

$2 sqrt{2} cos^2 frac{9 pi }{8} -sqrt{2} = sqrt{2}(2cos^2 frac{9 pi }{8} -1)=sqrt{2}cos frac{18 pi }{8}=sqrt{2}cos frac{9 pi }{4}=\ sqrt{2}cos(2 pi + frac{ pi }{4})=sqrt{2}cosfrac{ pi }{4}= sqrt{2} frac{ sqrt{2} }{2} =1$