## Algebra and Trigonometry 10th Edition

A = k$r^{2}$
If variables vary directly then y = x, so as one increases then the other increases. If variables vary inversely then y = $\frac{1}{x}$, as one increases the other decreases. In this example, A = k$r^{2}$ where k is a constant. This is the form since the variables are directly related and since r needs to be squared.