$$-3x^3+8x^3$$

$$\left(a+2x-3y\right)\left(a-2x+3y\right)$$

$$3y=\left(3\cos\left(x\right)+2x-5\right)^{21}$$

$$\int xe^{-6}dx$$

$$\left(\frac{2}{3}x^{3}+\frac{1}{2}y^{5}\right)^{2}$$

$$\:\frac{-104}{8}$$