# How do we get the integral sign below? [duplicate]

How do we get the integral sign below?

\documentclass{article}
your picture: $\displaystyle\int_a^b f(x)dx=F(b)-F(a)$
arguably nicer: $\displaystyle\int\limits_a^b f(x)\,\mathrm{d}x=F(b)-F(a)$