${\displaystyle L={\int }_a^{b}f(x)dx}$

${\displaystyle L={\int }_c^{d}f(y)dy}$

${\displaystyle L={\int }_a^{b}f(x)-g(x)dx}$

${\displaystyle L={\int }_c^{d}f(y)-g(y)dy}$