1. Find the surface area of a sphere
EXAMPLE 1
Find the surface area of a sphere
Find the surface area of the sphere.
SOLUTION
S = 4πr2
Formula for surface area of a sphere.
= 4π(82)
Substitute 8 for r.
= 256π
Simplify. ≈
Use a calculator.
The surface area of the sphere is about square
inches.
ANSWER

2. Standardized Test Practice
EXAMPLE 2
Standardized Test Practice
SOLUTION
S = 4πr2
Formula for surface area of a sphere.
20.25π = 4πr2
Substitute 20.25π for S.
= r2
Divide each side by 4π.
2.25 = r
Find the positive square root.

3. EXAMPLE 2
Standardized Test Practice
The diameter of the sphere is 2r = = 4.5
centimeters.
The correct answer is B.
ANSWER

4. 1. The diameter of a sphere is 40 feet. Find the
GUIDED PRACTICE
for Examples 1 and 2
1. The diameter of a sphere is 40 feet. Find the
surface area of the sphere.
S = 4πr2
Formula for surface area of a sphere.
= 4πr(20)2
Substitute 20 for r. =
Use a calculator.
The surface area of the sphere is about feet2
ANSWER

5. 2. The surface area of a sphere is 30π square meters.
GUIDED PRACTICE
for Examples 1 and 2
2. The surface area of a sphere is 30π square meters.
Find the radius of the sphere.
S = 4πr2
Formula for surface area of a sphere.
30π = 4πr2
Substitute 30π for S.
7.5 = r2
Divide each side by 4π.
2.71 = r
Find the positive square root.