## Algebra and Trigonometry 10th Edition

$cot^2u$
Use the identity: $cos^2u+sin^2u=1~~$ (Divide both sides by $sin^2u$) $\frac{cos^2u}{sin^2u}+\frac{sin^2u}{sin^2u}=\frac{1}{sin^2u}$ $cot^2u+1=csc^2u$