Question

Доказать тождество sin^3t*(1+ctgt)+cos^3t*(1+tgt)=sint+cost помогите

Answer 1

$sin^3t(1+ctgt)+cos^3t(1+tgt)=\\\\=sin^3t\cdot (1+ \frac{cost}{sint} )+cos^3t\cdot (1+\frac{sint}{cost})=\\\\=sin^3t\cdot \frac{sint+cost}{sint} +cos^3t\cdot \frac{sint+cost}{cost} =\\\\=sin^2t(sint+cost)+cos^2t(sint+cost)=\\\\=(sint+cost)(\underbrace {sin^2t+cos^2t}_{1})=sint+cost$