Question

Решите уравнение cos x2+ cos x= 0

Answer 1

cosx2+2cos²x2-1=0
cosx2=a
2a²+a-1=0
D=1+8=9
a1=(-1-3)/4=-1⇒cosx2=-1⇒x2=π+2πn⇒x=2π+4πn
a2=(-1+3)/4=1/2⇒cosx2=1/2⇒x2=+-π/3+2πn⇒x=+-2π/3+4πn