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

[latex]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} [/latex]