$\left(\cot^2a+1\right)\left(\cot^2a-1\right)=\csc^4a-2\csc^2a$

$8x-\left(15y+16z-12x\right)-\left(13x+20y\right)-\left(x+y+z\right)$

$\left(2a+5\right)\left(8a-1\right)$

$\frac{130^6}{130^4}$

$\left(x\right)\left(x\right)-2\left(x\right)\left(x\right)-\left(x\right)\left(x\right)$

$25x^2+20x+5$

$-2x^{-1}y^{-3}\left(2xy^3+x^{-2}y^{-3}\right)$