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=1 Cos(x-π/4)=1 (x-π/4)=2πn, n∈Z. x=π/4+2πn, n∈Z.