cosx+sinx=корень квадратный из двух.

Cosx+sinx=√2(1/√2)Cosx+(1/√2)sinx=√2·(1/√2)Cos(π/4)Cosx+sin(π/4)sinx=1Cos(x-π/4)=1(x-π/4)=2πn, n∈Z.x=π/4+2πn, n∈Z.