Solving Quadratic Equations with Square Roots

To find a circle's radius given it's area, we can look at the formula for the area of a circle. $$\begin{array}{c}A=\pi r^2\end{array}$$ In the case of our exercise, the area, $A,$ is $90{\text{cm}}^2$. We can set up our quadratic and solve for the radius, $r.$ Since we are computing length, we can disregard the negative root and say that the circle's radius, to the nearest tenth, is $5.4\text{cm}.$