Question

Соs^4 15^0-sin^4 15^0 вычислите

Answer 1

$cos^415а-sin^415а=(cos^215а-sin^215а)(underbrace{cos^215а+sin^215а}_{=1})=\ \ =cos^215а-sin^215а=cos(2cdot15а)=cos30а=frac{sqrt{3}}{2}$