User:Lihan161051/sandbox


 * $$\lim_{x\to 0}\frac{x}{x}=1$$

$$\sum_{n=1}^\infty \frac{1}{r^n} = \frac{1}{r-1}$$

$$\int_{10}^{13} 2x dx-\int_{0}^{3} 3x^2 dx$$