$$a^2+3ab-b^2+\frac{7ab^2-b^3}{2a-b}$$

$$x^3y-y^3$$

$$^{2t-1^3}$$

$$\left(a^3\right)^6-\left(a^2\right)^x$$

$$\frac{d^2}{dx^2}\left(3x^2e^x\right)$$

$$\left(y^2-6xy\right)^2$$

$$\frac{d}{dx}\left(3\tan\left(x\right)-\sec\left(x\right)\right)$$