Sin2a(1+ctg^2a)/1+cos2a

[latex]1+ctg^2 \alpha = \frac{1}{sin^2 \alpha } [/latex] [latex] \frac{sin2 \alpha(1+ctg^2 \alpha) }{1+cos2 \alpha }= \frac{2sin \alpha *cos \alpha }{1+2cos^2 \alpha -1}* \frac{1}{sin^2 \alpha }= \frac{sin \alpha }{cos \alpha } * \frac{1}{sin^2 \alpha }= \frac{1}{sin \alpha *cos \alpha } [/latex]