sin120+корень с 2*cos135

sin120°=sin(180°-60°)=sin60°=√3/2

cos135°=cos(180°-45°)=-cos45°=-√2/2

√3/2+√2·(-√2/2)=√3/2-√2·√2/2=√3/2-2/2=√3/2-1=(√3-2)/2