The equation in the image is:

$A = \pi r^2$

To isolate $r$, follow these steps:

1. Divide both sides of the equation by $\pi$: $\frac{A}{\pi} = r^2$

2. Take the square root of both sides to solve for $r$: $r = \sqrt{\frac{A}{\pi}}$

Thus, $r = \sqrt{\frac{A}{\pi}}$ is the expression for $r$ in terms of $A$.

Would you like more details or have any questions?

Here are 5 related questions:

1. What is the radius if the area $A$ is 100 square units?
2. How does changing the area $A$ affect the radius $r$?
3. What is the area if the radius $r$ is 5 units?
4. Can you express the diameter $d$ in terms of the area $A$?
5. What happens to the radius if the area is quadrupled?

Tip: When solving equations involving powers, always consider whether you need to take the square root, cube root, etc., to isolate variables.