Step by step
The question
Question: find the surface area of a sphere (a ball) with diameter 8.
1 Find the radius
The diameter goes all the way across the circle.
The radius is half of it.
Half of 8 is 8 divided by 2.
8 divided by 2 is 4.
So r = 4.
2 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 = 4.
4² means 4 times 4.
That is 16.
So S = 4 × π × 16.
4 times 16 is 64.
So S = 64π.
We keep π in the answer.
That is the exact answer.
3 About how much
To see about how much, put 3.14 for π.
64 times 3.14 is 200.96.
So the surface area is about 200.96 square units.
Let's look back.
First: find the radius.
Then: use the rule.
Last: about how much.