Question

Given a sphere with radius r, the formula 4r2 gives _____.

Answer 1

The answer is: The surface area of the sphere.

The explanations for this exercise is shown below:

By definition, the surface area of a sphere is four times the area of a circle.

You have that the area of a circle is:

$A=\pi r^{2}$

Where $r$ is the radius of the circle.

Therefore, to calculate the surface area of a sphere with radius $r$, you only need to multiply the equation shown above by four, as following:

$SA=4\pi r^{2}$