(sin x + cos x)² = 1+ sin x cos x
sin^2x+2sinxcosx+cos^2x=sin^2x+cos^2x+sinxcosx
sinxcosx=0
sinx=0; x=пk, k∈Z
cosx=0; x=п/2+пk, k∈Z
1+2sinxcosx=1+sinxcosx
sinxcosx=0
sinx=0
x=пn , n∈Z
cosx=0
x=п/2 +пn, n∈Z
x=пn/2
(sin x + cos x)² = 1+ sin x cos x
sin^2x+2sinxcosx+cos^2x=sin^2x+cos^2x+sinxcosx
sinxcosx=0
sinx=0; x=пk, k∈Z
cosx=0; x=п/2+пk, k∈Z