$$\lim_{x\to18}\left(\frac{x-81}{\sqrt{x}-9}\right)$$

$$\frac{4b^4-15b^2-4}{a^2-8a-20}$$

$$\sqrt[3]{3x}\cdot\sqrt[3]{2x}\cdot\sqrt[3]{16x^2}$$

$$\left(u-2\right)\left(-\frac{\left(5-4u\right)^{\frac{1}{2}}}{2}\right)$$

$$9\left(\frac{x}{3}\right)^8\left(-1\right)$$

$$\:\frac{\left(-8x\right)^2+\left(4x\right)^3+11x-4}{2x-1}$$

$$\lim_{x\to9}\left(\frac{\sqrt[5]{2x+14}-2}{\frac{1}{x}-\frac{11}{9}}\right)$$