Question

если sinx*cosx=1/5, то sin^4+cos^4=?

Answer 1

Нужно
(sinx)^4+(cosx)^4= ( (sinx)^2+(cosx)^2)^2 - 2* (sinx)^2*(cosx)^2= 1-2* ((sinx)*(cosx))^2=
1-2*(1/5)=1-2/5= 3/5