Common Core: 8th Grade Math : Geometry

Study concepts, example questions & explanations for Common Core: 8th Grade Math

varsity tutors app store varsity tutors android store

Example Questions

Example Question #26 : Apply The Pythagorean Theorem To Find The Distance Between Two Points In A Coordinate System: Ccss.Math.Content.8.G.B.8

Use the Pythagorean Theorem to calculate the length of the line shown on the provided coordinate plane. Round the answer to the nearest tenth.


10

Possible Answers:

\(\displaystyle 9.5\textup{ units}\)

\(\displaystyle 7.9\textup{ units}\)

\(\displaystyle 9.1\textup{ units}\)

\(\displaystyle 8.6\textup{ units}\)

\(\displaystyle 8.2\textup{ units}\)

Correct answer:

\(\displaystyle 8.6\textup{ units}\)

Explanation:

Notice that the diagonal line from the problem could be the hypotenuse of a right triangle. If we add two more lines, then we can create a closed figure in the shape of a triangle:

10 2

Let's use the Pythagorean Theorem to calculate the length of the line that represents the hypotenuse of a right triangle. The Pythagorean Theorem states that for right triangles:

\(\displaystyle a^2+b^2=c^2\)

In this equation:

\(\displaystyle a \textup{ and }b=\textup{legs}\)

\(\displaystyle c=\textup{hypotenuse}\)

We can count the number of units on the coordinate plane that were used to create the legs of our drawn triangle. Afterwards, we can use the Pythagorean Theorem to solve for the length of the hypotenuse, or the original diagonal line. 

In order to solve for this problem we want to substitute in the known side lengths for the triangle's legs:

\(\displaystyle 7^2+5^2=c^2\)

\(\displaystyle 49+25=c^2\)

\(\displaystyle 74=c^2\)

\(\displaystyle \sqrt{74}=\sqrt{c^2}\)

\(\displaystyle 8.6=c\)

Example Question #21 : Apply The Pythagorean Theorem To Find The Distance Between Two Points In A Coordinate System: Ccss.Math.Content.8.G.B.8

Use the Pythagorean Theorem to calculate the length of the line shown on the provided coordinate plane. Round the answer to the nearest tenth.


11

Possible Answers:

\(\displaystyle 10.5\textup{ units}\)

\(\displaystyle 11.1\textup{ units}\)

\(\displaystyle 10.8\textup{ units}\)

\(\displaystyle 11.3\textup{ units}\)

\(\displaystyle 10.3\textup{ units}\)

Correct answer:

\(\displaystyle 10.8\textup{ units}\)

Explanation:

Notice that the diagonal line from the problem could be the hypotenuse of a right triangle. If we add two more lines, then we can create a closed figure in the shape of a triangle:

11 2

Let's use the Pythagorean Theorem to calculate the length of the line that represents the hypotenuse of a right triangle. The Pythagorean Theorem states that for right triangles:

\(\displaystyle a^2+b^2=c^2\)

In this equation:

\(\displaystyle a \textup{ and }b=\textup{legs}\)

\(\displaystyle c=\textup{hypotenuse}\)

We can count the number of units on the coordinate plane that were used to create the legs of our drawn triangle. Afterwards, we can use the Pythagorean Theorem to solve for the length of the hypotenuse, or the original diagonal line. 

In order to solve for this problem we want to substitute in the known side lengths for the triangle's legs:

\(\displaystyle 4^2+10^2=c^2\)

\(\displaystyle 16+100=c^2\)

\(\displaystyle 116=c^2\)

\(\displaystyle \sqrt{116}=\sqrt{c^2}\)

\(\displaystyle 10.8=c\)

Example Question #28 : Apply The Pythagorean Theorem To Find The Distance Between Two Points In A Coordinate System: Ccss.Math.Content.8.G.B.8

Use the Pythagorean Theorem to calculate the length of the line shown on the provided coordinate plane. Round the answer to the nearest tenth.

12

Possible Answers:

\(\displaystyle 20.7\textup{ units}\)

\(\displaystyle 19.3\textup{ units}\)

\(\displaystyle 19.9\textup{ units}\)

\(\displaystyle 19.6\textup{ units}\)

\(\displaystyle 20.1\textup{ units}\)

Correct answer:

\(\displaystyle 20.1\textup{ units}\)

Explanation:

Notice that the diagonal line from the problem could be the hypotenuse of a right triangle. If we add two more lines, then we can create a closed figure in the shape of a triangle:

12 1

Let's use the Pythagorean Theorem to calculate the length of the line that represents the hypotenuse of a right triangle. The Pythagorean Theorem states that for right triangles:

\(\displaystyle a^2+b^2=c^2\)

In this equation:

\(\displaystyle a \textup{ and }b=\textup{legs}\)

\(\displaystyle c=\textup{hypotenuse}\)

We can count the number of units on the coordinate plane that were used to create the legs of our drawn triangle. Afterwards, we can use the Pythagorean Theorem to solve for the length of the hypotenuse, or the original diagonal line. 

In order to solve for this problem we want to substitute in the known side lengths for the triangle's legs:

\(\displaystyle 18^2+9^2=c^2\)

\(\displaystyle 324+81=c^2\)

\(\displaystyle 405=c^2\)

\(\displaystyle \sqrt{405}=\sqrt{c^2}\)

\(\displaystyle 20.1=c\)

Example Question #29 : Apply The Pythagorean Theorem To Find The Distance Between Two Points In A Coordinate System: Ccss.Math.Content.8.G.B.8

Susie walks north from her house to a park that is 30 meters away. Once she arrives at the park, she turns and walks west for 80 meters to a bench to feed some pigeons. She then walks north for another 30 meters to a concession stand. If Susie returns home in a straight line from the concession stand, how far will she walk from the concession stand to her house, in meters?

Possible Answers:

50

200

70

100

25

Correct answer:

100

Explanation:

Susie walks 30 meters north, then 80 meters west, then 30 meters north again. Thus, she walks 60 meters north and 80 meters west. These two directions are 90 degrees away from one another.

At this point, construct a right triangle with one leg that measures 60 meters and a second leg that is 80 meters.

You can save time by using the 3:4:5 common triangle. 60 and 80 are \(\displaystyle 3\cdot 20\) and \(\displaystyle 4\cdot 20\), respectively, making the hypotenuse equal to \(\displaystyle 5\cdot 20=100\).

We can solve for the length of the missing hypotenuse by applying the Pythagorean theorem:

\(\displaystyle a^{2}+b^{2}=c^{2}\)

Substitute the following known values into the formula and solve for the missing hypotenuse: side \(\displaystyle c\).

\(\displaystyle a= 60,\ b= 80,\ c= ?\)

\(\displaystyle (60)^{2}+(80)^{2}=c^{2}\)

 \(\displaystyle 3600+6400=c^{2}\)

\(\displaystyle 10,000=c^{2}\)

\(\displaystyle c=100\)

Susie will walk 100 meters to reach her house.

Example Question #6 : Volume Of A Three Dimensional Figure

Chestnut wood has a density of about \(\displaystyle 0.45\frac{g}{cm^3}\). A right circular cone made out of chestnut wood has a height of three meters, and a base with a radius of two meters. What is its mass in kilograms (nearest whole kilogram)?

Possible Answers:

\(\displaystyle 6,055 \; \textrm{kg}\)

\(\displaystyle 5,855 \; \textrm{kg}\)

\(\displaystyle 5,755 \; \textrm{kg}\)

\(\displaystyle 5,655 \; \textrm{kg}\)

\(\displaystyle 5,955 \; \textrm{kg}\)

Correct answer:

\(\displaystyle 5,655 \; \textrm{kg}\)

Explanation:

First, convert the dimensions to cubic centimeters by multiplying by \(\displaystyle 100\): the cone has height \(\displaystyle 300cm\), and its base has radius \(\displaystyle 200cm\).

\(\displaystyle 3m*\frac{100cm}{1m}=300cm\ \ \2m*\frac{100cm}{1m}=200cm\)

Its volume is found by using the formula and the converted height and radius.

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

\(\displaystyle V=\frac{1}{3} \pi (200cm)^{2} ( 300cm )\approx 12,566,371 \; \textrm{cm}^{3}\)

Now multiply this by \(\displaystyle 0.45\frac{g}{cm^3}\) to get the mass.

\(\displaystyle m=V*\rho\)

\(\displaystyle 12,566,371cm^3*0.45\frac{g}{cm^3} \approx 5,654,867g\)

Finally, convert the answer to kilograms.

\(\displaystyle 5654867g *\frac{1kg}{1,000g} \approx 5,655kg\)

Example Question #9 : Volume Of A Three Dimensional Figure

A cone has the height of 4 meters and the circular base area of 4 square meters. If we want to fill out the cone with water (density = \(\displaystyle 1000\frac{Kg}{m^3}\)), what is the mass of required water (nearest whole kilogram)?

Possible Answers:

\(\displaystyle 10,000\)

\(\displaystyle 4333\)

\(\displaystyle 5333\)

6333

\(\displaystyle 2133\)

Correct answer:

\(\displaystyle 5333\)

Explanation:

The volume of a cone is:

\(\displaystyle Volume=\frac{1}{3}\pi r^2h\)

where \(\displaystyle r\) is the radius of the circular base, and \(\displaystyle h\) is the height (the perpendicular distance from the base to the vertex).

 

As the circular base area is \(\displaystyle \pi r^2\), so we can rewrite the volume formula as follows:

 

\(\displaystyle Volume =\frac{A\times h}{3}\)

 

where \(\displaystyle A\) is the circular base area and known in this problem. So we can write:

 

\(\displaystyle Volume =\frac{A\times h}{3}=\frac{4\times 4}{3}=\frac{16}{3}\approx 5.333 m^3\)

 

We know that density is defined as mass per unit volume or:

 

\(\displaystyle \rho =\frac{m}{v}\)

 

Where \(\displaystyle \rho\) is the density; \(\displaystyle m\) is the mass and \(\displaystyle v\) is the volume. So we get:

 

\(\displaystyle m=\rho v=1000\times 5.333=5333 Kg\)

Example Question #7 : Volume Of A Three Dimensional Figure

The vertical height (or altitude) of a right cone is \(\displaystyle 2t\). The radius of the circular base of the cone is \(\displaystyle t\). Find the volume of the cone in terms of \(\displaystyle t\).

Possible Answers:

\(\displaystyle \frac{2}{3}\pi t^3\)

\(\displaystyle \frac{1}{3}\pi t^3\)

\(\displaystyle \frac{2}{3}\pi t^2\)

\(\displaystyle \pi t^3\)

\(\displaystyle \frac{1}{3}\pi t^2\)

Correct answer:

\(\displaystyle \frac{2}{3}\pi t^3\)

Explanation:

The volume of a cone is:

\(\displaystyle Volume=\frac{1}3{}\pi r^2h\)

 

where \(\displaystyle r\) is the radius of the circular base, and \(\displaystyle h\) is the height (the perpendicular distance from the base to the vertex).

 

\(\displaystyle Volume=\frac{1}3{}\pi r^2h =\frac{1}3{}\pi t^2\times 2t=\frac{2}{3}\pi t^3\)

Example Question #1 : Know And Use The Formulas For The Volumes Of Cones, Cylinders, And Spheres: Ccss.Math.Content.8.G.C.9

A right cone has a volume of \(\displaystyle 8\pi\), a height of \(\displaystyle 3t\) and a radius of the circular base of \(\displaystyle 2t\). Find \(\displaystyle t\).

Possible Answers:

\(\displaystyle \sqrt{2}\)

\(\displaystyle \sqrt[3]{3}\)

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

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

\(\displaystyle 2\)

Correct answer:

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

Explanation:

The volume of a cone is given by:

\(\displaystyle Volume=\frac{1}{3}\pi r^2h\)

where \(\displaystyle r\)is the radius of the circular base, and \(\displaystyle h\) is the height; the perpendicular distance from the base to the vertex. Substitute the known values in the formula:

 

\(\displaystyle Volume=\frac{1}{3}\pi r^2h\Rightarrow 8\pi=\frac{1}{3}\pi\times (2t)^2\times 3t\)

\(\displaystyle \Rightarrow 8\pi=4\pi t^3\Rightarrow t^3=2\Rightarrow t=\sqrt[3]{2}\)

Example Question #162 : Geometry

A cone has a diameter of \(\displaystyle 12\:m\) and a height of \(\displaystyle 4\:m\). In cubic meters, what is the volume of this cone?

Possible Answers:

\(\displaystyle 54\pi\:m^3\)

\(\displaystyle 36\pi\:m^3\)

\(\displaystyle 48\pi\:m^3\)

\(\displaystyle 144\pi\:m^3\)

Correct answer:

\(\displaystyle 48\pi\:m^3\)

Explanation:

First, divide the diameter in half to find the radius.

\(\displaystyle \frac{d}{2}=r\)

\(\displaystyle \frac{12}{2}=6\:m\)

Now, use the formula to find the volume of the cone.

\(\displaystyle \text{Volume}=\frac{1}{3}\pi r^2 h\)

\(\displaystyle \text{Volume}=\frac{1}{3}\pi \times 6^2\times4=\frac{1}{3}\pi \times 36\times4=\frac{144}{3}\pi=48\pi\:m^3\)

Example Question #2 : Know And Use The Formulas For The Volumes Of Cones, Cylinders, And Spheres: Ccss.Math.Content.8.G.C.9

The height of a cylinder is 3 inches and the radius of the circular end of the cylinder is 3 inches. Give the volume and surface area of the cylinder.

Possible Answers:

\(\displaystyle V=74.78 in^3, A=113.10in^2\)

\(\displaystyle V=74.78 in^3, A=103.04in^2\)

\(\displaystyle V=84.78 in^3, A=123.04in^2\)

\(\displaystyle V=84.82 in^3, A=113.10in^2\)

\(\displaystyle V=84.78 in^3, A=103.04in^2\)

Correct answer:

\(\displaystyle V=84.82 in^3, A=113.10in^2\)

Explanation:

The volume of a cylinder is found by multiplying the area of one end of the cylinder (base) by its height or:

 \(\displaystyle Volume=\pi r^2h\)

where \(\displaystyle r\) is the radius of the circular end of the cylinder and \(\displaystyle h\) is the height of the cylinder. So we can write:

 

\(\displaystyle Volume=\pi r^2h=\pi \times 3^2\times 3=84.82in^3\)

 

The surface area of the cylinder is given by:

 

\(\displaystyle A=2\pi r^2+2\pi rh\)

 

where \(\displaystyle A\) is the surface area of the cylinder, \(\displaystyle r\) is the radius of the cylinder and \(\displaystyle h\) is the height of the cylinder. So we can write:

\(\displaystyle A=2\pi r^2+2\pi rh\)

\(\displaystyle A=2\pi (3)^2+2\pi \times 3\times 3\)

\(\displaystyle A=18\pi+18\pi\)

\(\displaystyle A=36\pi\)

\(\displaystyle A=113.10\)

Learning Tools by Varsity Tutors