Sin^4 a - 2sin^2 a*cos^2 a + cos^4 a (sin a + cos a)^2Знак ^ возведение в степеньа -...

Решите задачу:

$\sin ^4a-2\sin^2a\cdot\cos^2a+\cos^4a=(\sin a+\cos a)^2\\\sin ^4a-2\sin^2a\cdot\cos^2a+\cos^4a=(\sin^2a-\cos^2a)^2\\(\sin^2a-\cos^2a)^2=(\sin a+\cos a)^2\\1=\cfrac{(\sin^2a-\cos^2a)^2}{(\sin a+\cos a)^2}=\cfrac{(\sin a -\cos a)^2(\sin a+\cos a)^2}{(\sin a+\cos a)^2}\\\sin^2-\sin 2a+\cos ^2a=1\\\sin 2a=-1\\2a=\cfrac{3\pi}{2}+2\pi n\\a=\cfrac{3\pi}{4}+\pi n,n\in\mathbb{Z}$