Question

Kak delat etu ☝ pomagitee

Answer 1

$cos^{2} alpha - sin^{2} alpha =cos(2* alpha )$

$cos^{2} frac{ pi }{8}- sin^{2} frac{ pi }{8}=cos(2* frac{ pi }{8})=cos frac{ pi }{4}= frac{ sqrt{2} }{2}$