$5-2.1x+17x$

$\left(2x^5+4y^2\right)^2$

$\frac{-12xy}{7y^4}.\frac{21x^5y^2}{4y}$

$\frac{1}{sec^2x}=\:cos^2x$

$\left(1+sin^2\theta\:\right)\left(1+cot^2\theta\:\right)$

$\left(20-30\right)\cdot4$

$3-\left[-2+11-\left(4-15-7\right)\right]-2+\left[-3\left(5-26-1\right)+2\right]$