McGraw Hill Integrated II, 2012
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McGraw Hill Integrated II, 2012 View details
6. Surface Areas and Volumes of Spheres
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Exercise 16 Page 852

To find the area of a hemisphere, calculate the area of half of a sphere with the same radius and add the area of the great circle.

122.2in^2

Practice makes perfect

A hemisphere is half of a sphere.

To find the area of a hemisphere we need to calculate the area of half of a sphere with the same radius and add the area of the great circle. Surface Area of a Hemisphere [0.8em] A=1/2(4Ï€ r^2)+Ï€ r^2 We first need to calculate the radius. To do so, we will consider the given fact that the area of a circle A of the great circle is 40 in^2. Let's recall the formula for the area. A=Ï€ r^2 We can substitute 40 for A in this formula and solve for the radius r.

A=Ï€ r^2
40=Ï€ r^2
â–¼
Solve for r
40/Ï€=r^2
r^2=40/Ï€
r^2=12.73...
r^2≈ 12.7
r≈ 3.56
r≈ 3.6

We know that r≈ 3.6in. We can substitute this value in the formula for the area of a hemisphere and simplify.

A=1/2(4Ï€ r^2)+Ï€ r^2
A=1/2(4Ï€ ( 3.6^2))+Ï€ ( 3.6^2)
â–¼
Evaluate right-hand side
A=1/2(4Ï€ (12.96))+Ï€ (12.96)
A=1/2(4(12.96)Ï€ )+12.96Ï€
A=1/2(51.84Ï€ )+12.96Ï€
A=51.84/2Ï€+12.96Ï€
A=25.92Ï€+12.96Ï€
A=38.88Ï€
A=122.145...
A≈ 122.2

The area of the hemisphere to the nearest tenth is 122.2in^2.