Корень из 50 cos 2 9п/8 минус корень из 50 sin 2 9п/8

√50cos²(9π/8)-√50sin²(9π/8)=√50(cos²(9π/8)-sin²(9π/8))=
=√50cos(2*9π/8)=√50cos(9π/4)=√50cos(2π+π/4)=
=√50cos(π/4)=√50*√2/2=√100 /2=10/2=5