PX275 - B2 - multiple integration

a r e a = \int_{y_{1}}^{y_{2}} \int_{x_{1}}^{x_{2}} d A

where, $d A = d x d y$

\begin{aligned} \bar{x} & = \frac{1}{a r e a} \iint x d A \\ \bar{x} & = \frac{1}{A} \int_{y_{1}}^{y_{2}} \int_{x_{1}}^{x_{2}} x d x d y \end{aligned}

\bar{y} = \frac{1}{A} \int_{y_{1}}^{y_{2}} \int_{x_{1}}^{x_{2}} y d x d y

\begin{aligned} \bar{x} & = \frac{1}{V o l} ∭ x d V \\ \bar{y} & = \frac{1}{V o l} ∭ y d V \\ \bar{z} & = \frac{1}{V o l} ∭ z d V \end{aligned}