cos2a/sin(a-π/4)=(2cos2a*cos(a-π/4)) /(2sin(a-π/4) cos(a-π/4)) cos2a/sin(a-π/4)=(2cos2a*cos(a-π/4)) /sin(2a-π/2) cos2a/sin(a-π/4)=-(2cos2a*cos(a-π/4)) /cos2a cos2a/sin(a-π/4)=-2*cos(a-π/4) ...