Surface area of sphere radius 3

Step by step

The question

Question: find the surface area of a sphere (a ball) with radius 3.

1 Use the rule

Cut the ball in half.

The flat circle inside has area π × r².

The skin of the ball covers exactly 4 of these circles.

Like the peel of an orange.

π is a special number for circles.

It is about 3.14.

So the surface area is S = 4 × π × r².

Now put the numbers in: r = 3.

3² means 3 times 3.

That is 9.

So S = 4 × π × 9.

4 times 9 is 36.

So S = 36π.

We keep π in the answer.

That is the exact answer.

2 About how much

To see about how much, put 3.14 for π.

36 times 3.14 is 113.04.

So the surface area is about 113.04 square units.

Let's look back.

First: use the rule.

Last: about how much.