$xy'-y=0$

$\int\left(2x\left(x^2+6\right)^{13}\right)dx$

$\int\frac{x}{\left(4-x^2\right)^2}dx$

$\frac{-\sin^2\left(x\right)+1-\cos\left(x\right)}{1-\cos\left(x\right)}=-\cos\left(x\right)$

$\frac{\cos\left(2a\right)}{\sin\left(a\right)}+\frac{\sin\left(2a\right)}{\cos\left(a\right)}$

$a^2-18a+23$

$9u^5-12u^4-21u^3$