$-9a^2b^3-6a^4b^6$

$\left(9a+5x\right)^2$

$\left(-4x^2-5x^5+3+7x\right)-\left(5x^3+8x^5-2\right)$

$4\cdot2-6-5\cdot3-7$

$\lim_{x\to0}\left(1-tan\left(2x\right)\right)^{\frac{1}{x}}$

$x\cdot\left(x^2+1\right)-3x\cdot\left(-x+3\right)+2\cdot\left(x^2-x\right)^2$

$\lim_{x\to1}\left(\frac{x^6-1}{x^2-1}\right)$