Answer
$V=\int_m^n A(x) \ dx$
See below.
Work Step by Step
The volume $V$ of a solid of integrable cross-sectional area $A(x)$ from $x=m$ to $x=n$ can be defined as the the integral of $A(x)$ from $m$ to $n$ and expressed as: $V=\int_m^n A(x) \ dx$
