Surface area of sphere radius 7

Step by step

The question

Question: find the surface area of a sphere (a ball) with radius 7.

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 = 7.

7² means 7 times 7.

That is 49.

So S = 4 × π × 49.

4 times 49 is 196.

So S = 196π.

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.

196 times 3.14 is 615.44.

So the surface area is about 615.44 square units.

Let's look back.

First: use the rule.

Last: about how much.