Пж2 cos^2 x-cosx-1=0

Question

Пж
2 cos^2 x-cosx-1=0

Answer 1

Y=cosx
2y²-1y-1=0
D=1+4*2=9
√D=3
y₁=(1-3)/4=-1/2
y₂=(1+3)/4=1
x₁=+-2π/3 +2πn
x₂=2πn
n целое