High School Math : Geometry

Study concepts, example questions & explanations for High School Math

varsity tutors app store varsity tutors android store

Example Questions

Example Question #142 : Solid Geometry

Find the surface area of a sphere whose diameter is \displaystyle D=\pi.

Possible Answers:

\displaystyle \pi ^{3}

\displaystyle 37.7

Correct answer:

\displaystyle \pi ^{3}

Explanation:

The surface area of a sphere is found by the formula \displaystyle SA=4\pi r^{2}. We need to first convert the given diameter of \displaystyle D=\pi to the sphere's radius.

\displaystyle D=2r

\displaystyle \pi =2r

\displaystyle r=\pi/2

Now, we can solve for surface area.

\displaystyle =4\pi \cdot \frac{\pi^{2} }{4}

Example Question #1 : How To Find The Surface Area Of A Sphere

To the nearest tenth of a square centimeter, give the surface area of a sphere with volume 1,000 cubic centimeters.

Possible Answers:

\displaystyle 333.3 \textrm{ cm}^{2}

\displaystyle 314.2 \textrm{ cm}^{2}

\displaystyle 708.3 \textrm{ cm}^{2}

\displaystyle 120.9 \textrm{ cm}^{2}

\displaystyle 483.6 \textrm{ cm}^{2}

Correct answer:

\displaystyle 483.6 \textrm{ cm}^{2}

Explanation:

The volume of a sphere in terms of its radius \displaystyle r is 

\displaystyle V = \frac{4\pi r^3}{3}

Substitute \displaystyle V = 1,000 and solve for \displaystyle r:

\displaystyle \frac{4\pi r^3}{3} = V

\displaystyle \frac{4\pi r^3}{3} = 1,000

\displaystyle \frac{4\pi r^3}{3}\cdot \frac{3}{4\pi }= 1,000\cdot \frac{3}{4\pi }

\displaystyle r^3= \frac{3,000}{4\pi }

\displaystyle r=\sqrt[3]{ \frac{3,000}{4\pi }} \approx 6.20 \textrm{ cm }

Substitute for \displaystyle r in the formula for the surface area of a sphere:

\displaystyle A = 4\pi r^2 \approx 4 \cdot \pi \cdot 6.20 ^2 \approx 483.6 \textrm{ cm}^{2}

Example Question #1 : How To Find The Surface Area Of A Sphere

Find the surface area of a sphere with a radius of \displaystyle 4

Possible Answers:

\displaystyle 4\Pi

\displaystyle 36\Pi

\displaystyle 42\Pi

\displaystyle 64\Pi

\displaystyle 16\Pi

Correct answer:

\displaystyle 64\Pi

Explanation:

The standard equation to find the area of a sphere is \displaystyle 4\Pi r^2.

Substitute the given radius into the standard equation to get the answer:

\displaystyle 4\Pi (4)^2=4\Pi (16)=64\Pi

Example Question #681 : Geometry

Given that the radius of a sphere is 3, find the surface area. 

Possible Answers:

\displaystyle 9\pi

\displaystyle 12\pi

\displaystyle 16\pi

\displaystyle 4\pi

\displaystyle 36\pi

Correct answer:

\displaystyle 36\pi

Explanation:

The standard equation to find the area of a sphere is 

\displaystyle SA=4\pi r^2

where \displaystyle r denotes the radius. Plug in the given radius to find the surface area. 

\displaystyle SA=4\pi (3)^2=4\cdot 9\cdot \pi =36\pi

Example Question #1 : How To Find The Surface Area Of A Sphere

Find the surface area of the following sphere.

Sphere

Possible Answers:

\displaystyle 145 \pi m^2

\displaystyle 160 \pi m^2

\displaystyle 130 \pi m^2

\displaystyle 144 \pi m^2

\displaystyle 124 \pi m^2

Correct answer:

\displaystyle 144 \pi m^2

Explanation:

The formula for the surface area of a sphere is:

\displaystyle SA = 4 \pi r^2

where \displaystyle r is the radius of the sphere.

 

Plugging in our values, we get:

\displaystyle SA = 4 \pi (6m)^2

\displaystyle SA = 4 \pi (36m) = 144 \pi m^2

Example Question #141 : Solid Geometry

Find the surface area of the following sphere.

Sphere

Possible Answers:

\displaystyle 324 \pi m^2

\displaystyle 344 \pi m^2

\displaystyle 304 \pi m^2

\displaystyle 334 \pi m^2

\displaystyle 314 \pi m^2

Correct answer:

\displaystyle 324 \pi m^2

Explanation:

The formula for the surface area of a sphere is:

\displaystyle SA = 4 \pi (r^2)

Where \displaystyle r is the radius of the sphere

 

Plugging in our values, we get:

\displaystyle SA = 4 \pi (9m)^2

\displaystyle SA = 324 \pi m^2

Example Question #1 : How To Find The Surface Area Of A Sphere

What is the surface area of a composite figure of a cone and a sphere, both with a radius of 5 cm, if the height of the cone is 12 cm? Consider an ice cream cone as an example of the composite figure, where half of the sphere is above the edge of the cone.

Possible Answers:

\displaystyle 115\pi\ cm^2

\displaystyle 50\pi\ cm^2

\displaystyle 165\pi\ cm^2

\displaystyle 65\pi\ cm^2

\displaystyle 125\pi\ cm^2

Correct answer:

\displaystyle 115\pi\ cm^2

Explanation:

Calculate the slant height height of the cone using the Pythagorean Theorem. The height will be the height of the cone, the base will be the radius, and the hypotenuse will be the slant height.

\displaystyle s^2=r^2+h^2

\displaystyle s^2=(5)^2+(12)^2=25+144=169

\displaystyle s=\sqrt{169}=13

The surface area of the cone (excluding the base) is given by the formula \displaystyle A=\pi rs. Plug in our values to solve.

\displaystyle A_{cone}=\pi(5)(13)=65\pi\ cm^2

The surface area of a sphere is given by \displaystyle A=4\pi r^2 but we only need half of the sphere, so the area of a hemisphere is \displaystyle A=2\pi r^2.

\displaystyle A_{hemisphere}=2\pi(5)^2=50\pi\ cm^2

So the total surface area of the composite figure is \displaystyle 65\pi\ cm^2+50\pi\ cm^2=115\pi\ cm^2.

Example Question #791 : Geometry

What is the surface area of a hemisphere with a diameter of 4\ cm\displaystyle 4\ cm?

Possible Answers:

\displaystyle 18\pi \ cm^{2}

\displaystyle 12\pi \ cm^{2}

\displaystyle 8\pi \ cm^{2}

\displaystyle 16\pi \ cm^{2}

\displaystyle 20\pi \ cm^{2}

Correct answer:

\displaystyle 12\pi \ cm^{2}

Explanation:

A hemisphere is half of a sphere.  The surface area is broken into two parts:  the spherical part and the circular base. 

The surface area of a sphere is given by SA = 4\pi r^{2}\displaystyle SA = 4\pi r^{2}.

So the surface area of the spherical part of a hemisphere is SA = 2\pi r^{2}\displaystyle SA = 2\pi r^{2}

The area of the circular base is given by A = \pi r^{2}\displaystyle A = \pi r^{2}.  The radius to use is half the diameter, or 2 cm.

Example Question #682 : Geometry

What is the surface area of a sphere with a radius of \displaystyle 12?

Possible Answers:

\displaystyle 576

\displaystyle 24\pi

\displaystyle 144\pi

\displaystyle 288\pi

\displaystyle 576\pi

Correct answer:

\displaystyle 576\pi

Explanation:

To solve for the surface area of a sphere you must remember the formula:

First, plug the radius into the equation for \displaystyle r:

\displaystyle SA=(4)(12^{2})(\pi)

Since \displaystyle (12^{2})=144, the surface area is \displaystyle (4)(144)(\pi)=576\pi.

The answer is therefore \displaystyle 576\pi.

Example Question #1 : How To Find The Diameter Of A Sphere

What is the diameter of a sphere with a volume of \displaystyle 36\pi?

Possible Answers:

\displaystyle 27

\displaystyle 3

\displaystyle 6

\displaystyle 9

Correct answer:

\displaystyle 6

Explanation:

To find the diameter of a sphere we must use the equation for the volume of a sphere to find the radius which is half of the diameter.

The equation is

First we enter the volume into the equation yielding \displaystyle 36\pi=(\frac{4}{3})(\pi)(r^{3})

We then divide each side by  to get \displaystyle 36=(\frac{4}{3})(r^{3})

We then multiply each side by  to get \displaystyle 27=r^{3}

We then take the cubic root of each side to solve for the radius \displaystyle \sqrt[3]{27}=\sqrt[3]{r^{3}}

The radius is \displaystyle r=3

We then multiply the radius by 2 to find the diameter \displaystyle 3*2=6

The answer for the diameter is \displaystyle 6.

Learning Tools by Varsity Tutors