Find the surface area of a sphere

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Presentation transcript:

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. ≈ 804.25 Use a calculator. The surface area of the sphere is about 804.25 square inches. ANSWER

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. 5.0625 = r2 Divide each side by 4π. 2.25 = r Find the positive square root.

EXAMPLE 2 Standardized Test Practice The diameter of the sphere is 2r = 2 2.25 = 4.5 centimeters. The correct answer is B. ANSWER

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. = 5028.56 Use a calculator. The surface area of the sphere is about 5028.56 feet2 ANSWER

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.