Question

Find the length of the radius of a sphere with a surface area of 78.54 km2.
A. 5 ft
B. 15 ft
C. 10 ft
D. 2.5 ft

Answer 1

The equation for Surface Area of a Sphere is given by:\[\huge A=4\pi r^2\]
In this problem they gave us A, and we need to solve for r.
\[\huge 78.54=4 \pi r^2\]Divide both sides by 4pi:\[\huge \frac{78.54}{4 \pi}=r^2\]Then, to solve for r, simply take the square root of both sides, yay!!

Answer 2

how do you that?

Answer 3

With a calculator of course!! ^^
If you don't have a Pi button on your calculator, then use 3.14 instead.
Having trouble with which part? :O the square root step?