Chapter 9 - Solving Quadratic Equations - 9.3 - Solving Quadratic Equations Using Square Roots - Monitoring Progress - Page 500: 11

$r=\frac12\sqrt{\frac{S}{\pi}}$ $r\approx 8$ in

$$S=4\pi r^2$$ $$r^2=\frac{S}{4\pi}$$ $$r=\pm\sqrt{\frac{S}{4\pi}}=\pm\frac12\sqrt{\frac{S}{\pi}}$$ Take the positive value: $$r=\frac12\sqrt{\frac{S}{\pi}}$$ Substitute $S=804$: $$r=\frac12\sqrt{\frac{804}{\pi}}\approx 8\text{ in}$$