Find the value of F (x) = cos ^ 2-2sinxcosx-sin ^ 2x X which belongs to [0, π / 2] Answer in an hour

Find the value of F (x) = cos ^ 2-2sinxcosx-sin ^ 2x X which belongs to [0, π / 2] Answer in an hour

f(x)=cos^2-2sinxcosx-sin^2x
=cos2x -sin2x
=Radical 2cos (2x + π / 4)
Because 0