High School Math : Solid Geometry

Study concepts, example questions & explanations for High School Math

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Example Questions

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

Find the surface area of the following polyhedron.

Ice_cream_cone

Possible Answers:

\(\displaystyle 118 \pi m^2\)

\(\displaystyle 98 \pi m^2\)

\(\displaystyle 88 \pi m^2\)

\(\displaystyle 108 \pi m^2\)

\(\displaystyle 128 \pi m^2\)

Correct answer:

\(\displaystyle 108 \pi m^2\)

Explanation:

The formula for the surface area of the polyhedron is:

\(\displaystyle SA = SA_{cone}+\frac{1}{2}SA_{sphere}\)

\(\displaystyle SA = \pi r l+\frac{1}{2}(4 \pi r^2)\)

\(\displaystyle SA = \pi r l+2 \pi r^2\)

Where \(\displaystyle r\) is the radius of the cone, \(\displaystyle l\) is the slant height of the cone, and \(\displaystyle r\) is the radius of the sphere

 

Use the formula for a \(\displaystyle 30-60-90\) triangle to find the radius and slant height:

\(\displaystyle a-a\sqrt{2}-2a\)

\(\displaystyle 3\sqrt{3}m-9m-6\sqrt{3}m\)

 

Plugging in our values, we get:

\(\displaystyle SA = \pi r l+2 \pi r^2\)

\(\displaystyle SA = (\pi)(3\sqrt{3}m)(6\sqrt{3}m)+2(\pi)(3\sqrt{3}m)^2\)

\(\displaystyle SA = 54 \pi m^2 + 54 \pi m^2 = 108 \pi m^2\)

Example Question #3 : Other Polyhedrons

Find the surface area of the following polyhedron.

Dome

Possible Answers:

\(\displaystyle 81 \pi m^2\)

\(\displaystyle 101 \pi m^2\)

\(\displaystyle 61 \pi m^2\)

\(\displaystyle 91 \pi m^2\)

\(\displaystyle 71 \pi m^2\)

Correct answer:

\(\displaystyle 81 \pi m^2\)

Explanation:

The formula for the surface area of the polyhedron is:

\(\displaystyle SA = (cone:no\ base)+(cylinder:one\ base)\)

\(\displaystyle SA = \frac{1}{2}(circumference)(slant\ height)+(base)+(circumference)(height)\)

\(\displaystyle SA = \frac{1}{2}(2 \pi r)(h_s)+(\pi r^2)+(2 \pi r)(h)\)

where \(\displaystyle r\) is the radius of the cone, \(\displaystyle h_s\) is the slant height of the cone, \(\displaystyle r\) is the radius of the cylinder, and \(\displaystyle h\) is the height of the cylinder.

 

Use the formula for a \(\displaystyle 30-60-90\) triangle to find the length of the radius:

\(\displaystyle a-a\sqrt{3}-2a\)

\(\displaystyle 3m-3\sqrt{3}m-6m\)

 

Plugging in our values, we get:

\(\displaystyle SA = \frac{1}{2}(2\pi (3m))(6m)+(\pi)(3m)^2+(2\pi (3m)(9m))\)

\(\displaystyle SA = 81 \pi m^2\)

Example Question #2 : How To Find The Surface Area Of A Polyhedron

Find the surface area of the following polyhedron.

Ice_cream_cone

Possible Answers:

\(\displaystyle 64\sqrt{2}\pi + 32 \pi m^2\)

\(\displaystyle 32\sqrt{2}\pi + 32 \pi m^2\)

\(\displaystyle 64\sqrt{2}\pi + 64 \pi m^2\)

\(\displaystyle 32\sqrt{2}\pi + 64 \pi m^2\)

Correct answer:

\(\displaystyle 32\sqrt{2}\pi + 64 \pi m^2\)

Explanation:

The formula for the surface area of a polyhedron is:

\(\displaystyle SA = (cone)+ \frac{1}{2}(sphere)\)

\(\displaystyle SA = \frac{1}{2}(2\pi r)(h_s)+ \frac{1}{2}(4\pi r^2)\)

\(\displaystyle SA = \pi rh_s+ 2\pi r^2\)

where \(\displaystyle r\) is the radius of the polyhedron and \(\displaystyle h_s\) is the slant height of the cone.

 

Use the formula for a \(\displaystyle 45-45-90\) triangle to find the length of the radius:

\(\displaystyle a-a-a\sqrt{2}\)

\(\displaystyle 4\sqrt{2}m-4\sqrt{2}m-8m\)

 

Plugging in our values, we get:

\(\displaystyle SA = \pi (4\sqrt{2}m)(8m)+ 2\pi (4\sqrt{2}m)^2\)

\(\displaystyle SA = 32\sqrt{2}\pi + 64 \pi m^2\)

Example Question #21 : Solid Geometry

Find the volume of the following half cylinder.

Half_cylinder

Possible Answers:

\(\displaystyle 207.5 \pi m^3\)

\(\displaystyle 187.5 \pi m^3\)

\(\displaystyle 157.5 \pi m^3\)

\(\displaystyle 200 \pi m^3\)

\(\displaystyle 150.5 \pi m^3\)

Correct answer:

\(\displaystyle 187.5 \pi m^3\)

Explanation:

The formula for the volume of a half-cylinder is:

\(\displaystyle V = \frac{1}{2} (\pi r^2 h)\)

where \(\displaystyle r\) is the radius of the base and \(\displaystyle h\) is the length of the height.

 

Plugging in our values, we get:

\(\displaystyle V = \frac{1}{2} \pi (5m)^2 (15m)\)

\(\displaystyle V = 187.5 \pi m^3\)

Example Question #6 : Other Polyhedrons

Find the volume of the following polyhedron.

Ice_cream_cone

Possible Answers:

\(\displaystyle 81 \pi m^3+54\sqrt{3} \pi m^3\)

\(\displaystyle 54 \pi m^3+81\sqrt{3} \pi m^3\)

\(\displaystyle 81 \pi m^3+81\sqrt{3} \pi m^3\)

\(\displaystyle 81 \pi m^3+50\sqrt{3} \pi m^3\)

\(\displaystyle 54 \pi m^3+54\sqrt{3} \pi m^3\)

Correct answer:

\(\displaystyle 81 \pi m^3+54\sqrt{3} \pi m^3\)

Explanation:

The formula for the volume of the polyhedron is:

\(\displaystyle V = V_{cone}+\frac{1}{2}V_{sphere}\)

\(\displaystyle V = \frac{\pi r^2 h}{3} +\frac{1}{2} \frac{4\pi r^3}{3}\)

\(\displaystyle V = \frac{\pi r^2 h}{3} +\frac{2\pi r^3}{3}\)

Where \(\displaystyle r\) is the radius of the cone, \(\displaystyle h\) is the height of the cone, and \(\displaystyle r\) is the radius of the sphere.

 

Use the formula for a \(\displaystyle 30-60-90\) triangle to find the length of the radius:

\(\displaystyle a-a\sqrt{2}-2a\)

\(\displaystyle 3\sqrt{3}m-9m-6\sqrt{3}m\)

 

Plugging in our values, we get:

\(\displaystyle V = \frac{\pi (3\sqrt{3}m)^29m}{3}+\frac{2 \pi (3\sqrt{3}m)^3}{3}\)

\(\displaystyle V = \frac{\pi (27m^2)9m}{3}+\frac{2 \pi (81\sqrt{3}m^3)}{3}\)

\(\displaystyle V = 81 \pi m^3+54\sqrt{3} \pi m^3\)

Example Question #22 : Solid Geometry

Find the volume of the following polyhedron.

Dome

Possible Answers:

\(\displaystyle 18 \pi \sqrt{3}m^3 + 81 \pi m^3\)

\(\displaystyle 24 \pi \sqrt{3}m^3 + 81 \pi m^3\)

\(\displaystyle 6 \pi \sqrt{3}m^3 + 81 \pi m^3\)

\(\displaystyle 9 \pi \sqrt{3}m^3 + 81 \pi m^3\)

\(\displaystyle 27 \pi \sqrt{3}m^3 + 81 \pi m^3\)

Correct answer:

\(\displaystyle 9 \pi \sqrt{3}m^3 + 81 \pi m^3\)

Explanation:

The formula for the volume of the polyhedron is:

\(\displaystyle V = (cone)+(cylinder)\)

\(\displaystyle V = \frac{\pi r^2 h}{3}+\pi r^2 h\)

where \(\displaystyle r\) is the radius of the cone, \(\displaystyle h\) is the height of the cone, \(\displaystyle r\) is the radius of the cylinder, and \(\displaystyle h\) is the height of the cylinder.

 

Use the formula for a \(\displaystyle 30-60-90\) triangle to find the length of the radius and height of the cone:

\(\displaystyle a-a\sqrt{3}-2a\)

\(\displaystyle 3m-3\sqrt{3}m-6m\)

 

Plugging in our values, we get:

\(\displaystyle V = \frac{\pi (3m)^2 (3\sqrt{3}m)}{3}+\pi (3m)^2 (9m)\)

\(\displaystyle V = 9 \pi \sqrt{3}m^3 + 81 \pi m^3\)

Example Question #8 : Other Polyhedrons

Find the volume of the following polyhedron.

Ice_cream_cone

Possible Answers:

\(\displaystyle 128 \sqrt{2} \pi m^3\)

\(\displaystyle 108 \sqrt{2} \pi m^3\)

\(\displaystyle 118 \sqrt{2} \pi m^3\)

\(\displaystyle 138 \sqrt{2} \pi m^3\)

\(\displaystyle 148 \sqrt{2} \pi m^3\)

Correct answer:

\(\displaystyle 128 \sqrt{2} \pi m^3\)

Explanation:

The formula for the volume of the polyhedron is:

\(\displaystyle V = (cone) + \frac{1}{2}(sphere)\)

\(\displaystyle V = \frac{1}{3}(\pi r^2)(h)+\frac{1}{2}\left(\frac{4\pi r^3}{3}\right)\)

where \(\displaystyle r\) is the radius of the polyhedron and \(\displaystyle h\) is the height of the cone.

 

Use the formula for a \(\displaystyle 45-45-90\) triangle to find the length of the radius and height:

\(\displaystyle a-a-a\sqrt{2}\)

\(\displaystyle 4\sqrt{2}m-4\sqrt{2}m-8m\)

 

Plugging in our values, we get:

\(\displaystyle V = \frac{1}{3}(\pi (4\sqrt{2}m)^2)(4\sqrt{2}m)+\frac{1}{2}\left(\frac{4\pi (4\sqrt{2}m)^3}{3}\right)\)

\(\displaystyle V = 128 \sqrt{2} \pi m^3\)

Example Question #643 : Geometry

Our backyard pool holds 10,000 gallons.  Its average depth is 4 feet deep and it is 10 feet long.  If there are 7.48 gallons in a cubic foot, how wide is the pool? 

Possible Answers:

133 ft  

 33  ft   

7.48 ft  

100 ft  

30 ft  

Correct answer:

 33  ft   

Explanation:

There are 7.48 gallons in cubic foot. Set up a ratio:

1 ft3 / 7.48 gallons = x cubic feet / 10,000 gallons

Pool Volume = 10,000 gallons = 10,000 gallons * (1 ft3/ 7.48 gallons) = 1336.9 ft3

Pool Volume = 4ft x 10 ft x WIDTH = 1336.9 cubic feet

Solve for WIDTH:

4 ft x 10 ft x WIDTH = 1336.9 cubic feet

WIDTH = 1336.9 / (4 x 10) = 33.4 ft

Example Question #11 : Solid Geometry

A cube has a volume of 64cm3. What is the area of one side of the cube?

Possible Answers:

16cm

16cm3

16cm2

4cm

4cm2

Correct answer:

16cm2

Explanation:

The cube has a volume of 64cm3, making the length of one edge 4cm (4 * 4 * 4 = 64).

So the area of one side is 4 * 4 = 16cm2

Example Question #2 : How To Find The Length Of An Edge Of A Cube

Given that the suface area of a cube is 72, find the length of one of its sides. 

Possible Answers:

\(\displaystyle 6\)

\(\displaystyle 2\sqrt{3}\)

\(\displaystyle 3\)

\(\displaystyle 3\sqrt{2}\)

\(\displaystyle \sqrt{6}\)

Correct answer:

\(\displaystyle 2\sqrt{3}\)

Explanation:

The standard equation for surface area is 

\(\displaystyle SA=6a^2\)

where \(\displaystyle a\) denotes side length. Rearrange the equation in terms of \(\displaystyle a\) to find the length of a side with the given surface area:

\(\displaystyle a=\sqrt{\frac{SA}{6}}=\sqrt{\frac{72}{6}}=\sqrt{12}=2\sqrt{3}\)

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