$$\lim_{x\to0}\left(\frac{\sqrt{n^2+1}}{n^3}\right)$$

$$-\frac{3}{x}+\frac{1}{x^2}$$

$$xy-4x+y=4$$

$$x^2-15x-56$$

$$\frac{2x^3+2x-1}{x-3}$$

$$\frac{x}{12.65}+3.99=130.49$$

$$\left(4x^2+6\right)\left(4x^2-6\right)$$