Code:
$\int_{0}^{10} 2x^2+4\:dx$
$\int_{0}^{10} 2x^2+4\:dx$
This \: adds a space.
If you add \displaystyle the integral sign (or some other notation, like fractions) is going to get bigger as for a display.
Code:
$\displaystyle \int_{0}^{10} 2x^2+4\:dx$
$\displaystyle \int_{0}^{10} 2x^2+4\:dx$
Two dollar sign from both sides assign \displaystyle automatically (also it usually centers the expression, but in the case of this forum it just leaves more blank space to the left)
Code:
$$\int_{0}^{10} 2x^2+4\:dx$$
$$\int_{0}^{10} 2x^2+4\:dx$$
Code:
$$\int_{0}^{10} 2x^2+4\:\text{d}x$$
$$\int_{0}^{10} 2x^2+4\:\text{d}x$$
Code:
$\sum_{n=1}^{\infty} 2^{n}$
$\sum_{n=1}^{\infty} 2^{n}$
Code:
$$\sum_{n=1}^{\infty} 2^{n}$$
$$\sum_{n=1}^{\infty} 2^{n}$$