$\csc^2\left(21\right)-\cot^2\left(21\right)$

$\cot^2x+\csc^2x=4$

$y'+\cot\left(x\right)y=2x\csc\left(x\right)$

$\ln\frac{x^2}{1+x^2}$

$\frac{1}{2}x\frac{2}{4}$

$\frac{\tan\left(x\right)}{1-\cos\left(w\right)}=\csc\left(x\right)\left(1-\sec\left(x\right)\right)$