1. cos(x/2)=√2/2
x/2=+-arccos(√2/2)+2πn, n∈Z
x/2=+-π/4+2πn, n∈Z |*2
x=+-π/2+4πn, n∈Z
2. cos²x=sin²x
cos²x-sin²x=0
cos2x=0
2x=π/2+2πn, n∈Z |:2
x=π/4+πn, n∈Z
3. sinx+sin2x=0
sinx+2sinx*cosx=0
sinx(1+2cosx)=0
sinx=0 или 1+2cosx=0
x₁=πn, n∈Z cosx=-1/2
x=+-arccos(-1/2)+2πn, n∈Z
x=+-(π-arccox(1/2))+2πn, n∈Z
x=+-(π-π/3)+2πn, n∈Z
x₂=+-2π/3+2πn, n∈Z