$$9n^6-18n^3+n^6$$

$$\left(\frac{2x^4yz^2}{7}\right)\left(\frac{7xy^2z^4}{6}\right)$$

$$\frac{2a+2}{a^2-3a-4}$$

$$x^4-3x^2+1$$

$$\int\left(\frac{3}{x\left(2-\sqrt{x}\right)}\right)dx$$

$$5b\left(a^2+4ab\right)$$

$$\left(-4x+6y-20\right)-\left(6x+4y+12\right)$$