Question

(sinx+cosx)^2 = 1+sinx * cosx

Answer 1

(sin x + cos x)^2=1+sin (x) * cos(x)
 
(sin x + cos x)^2=cos^2(x) + 2cos(x) sin(x)+sin^2(x)
cos^2(x) + 2cos(x) sin(x)+sin^2(x)=1+cos(x) * sin (x)
1+cos(x) * sin (x)= -1+cos^2(x)+cos(x) * sin (x)+sin^2(x) = 0
1/2sin2x=0
sin2x=0
2x=(Pi) n         n принадлежит Z
x=((Pi) * n)/2               n принадлежит Z