## Algebra and Trigonometry 10th Edition

F = $\frac{k{m_{1}}{m_{2}}}{r^{2}}$
If variables vary directly then y = x, so as one increases the other increases. If variables vary inversely then y = $\frac{1}{x}$, so as one increases the other decreases. If variables vary jointly, then the variables are directly proportional, so y = x. Using the description, F = $\frac{k{m_{1}}{m_{2}}}{r^{2}}$ where k is a constant.