Question

Обчисліть cos^4a+sin^4a, якщо sin^2a=2/3

Answer 1

$cos^2 alpha = 1-sin^2 alpha =1- frac{2}{3} = frac{1}{3} \ \ cos^4 alpha +sin^4 alpha =(cos^2 alpha )^2+(sin^2 alpha )^2= \ \ =( frac{1}{3} )^2+( frac{2}{3} )^2= frac{1}{9}+ frac{4}{9}= frac{5}{9}$