GED Math : Geometry and Graphs

Study concepts, example questions & explanations for GED Math

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Example Questions

Example Question #131 : 2 Dimensional Geometry

Let \(\displaystyle \pi = 3.14\)

Find the area of a circle with a diameter of 14cm.

Possible Answers:

\(\displaystyle 43.96\text{cm}^2\)

\(\displaystyle 153.86\text{cm}^2\)

\(\displaystyle 200.96\text{cm}^2\)

\(\displaystyle 87.92\text{cm}^2\)

\(\displaystyle 615.44\text{cm}^2\)

Correct answer:

\(\displaystyle 153.86\text{cm}^2\)

Explanation:

To find the area of a circle, we will use the following formula:

\(\displaystyle A = \pi \cdot r^2\)

where r is the radius of the circle. 

Now, we know \(\displaystyle \pi = 3.14\). We know the diameter of the circle is 14cm. We also know the diameter is two times the radius. Therefore, the radius is 7cm. So, we can substitute. We get

\(\displaystyle A = 3.14 \cdot (7\text{cm})^2\)

\(\displaystyle A = 3.14 \cdot 49\text{cm}^2\)

\(\displaystyle A = 153.86\text{cm}^2\)

Example Question #132 : 2 Dimensional Geometry

Find the area of a circle with a diameter of \(\displaystyle 10\pi\).

Possible Answers:

\(\displaystyle 50\pi\)

\(\displaystyle 10\)

\(\displaystyle 25\pi ^2\)

\(\displaystyle 100\pi^4\)

\(\displaystyle 25\pi ^3\)

Correct answer:

\(\displaystyle 25\pi ^3\)

Explanation:

Write the formula for the area of a circle.

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

The radius is half the diameter.  Multiply the radius by one half.

\(\displaystyle 10\pi \cdot \frac{1}{2} = 5\pi\)

Substitute the radius into the equation.

\(\displaystyle A=\pi (5\pi)^2 = \pi (5\pi)(5\pi) = 25\pi ^3\)

The answer is:  \(\displaystyle 25\pi ^3\)

Example Question #133 : 2 Dimensional Geometry

Determine the area of a circle with a diameter of \(\displaystyle \frac{5}{3}\).

Possible Answers:

\(\displaystyle \frac{25}{18}\pi\)

\(\displaystyle \frac{100}{9}\pi\)

\(\displaystyle \frac{5}{18}\pi\)

\(\displaystyle \frac{25}{36}\pi\)

\(\displaystyle \frac{25}{9}\pi\)

Correct answer:

\(\displaystyle \frac{25}{36}\pi\)

Explanation:

Write the formula for the area of a circle.

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

The radius is half the diameter.  Multiply the diameter by half.

\(\displaystyle \frac{5}{3}\cdot \frac{1}{2} = \frac{5}{6}\)

Substitute the radius into the equation.

\(\displaystyle A=\pi (\frac{5}{6})^2= \pi (\frac{5}{6})(\frac{5}{6}) = \frac{25}{36}\pi\)

The answer is:  \(\displaystyle \frac{25}{36}\pi\)

Example Question #131 : Circles

Find the area of a circle with a radius of 12.

Possible Answers:

\(\displaystyle 144\pi^2\)

\(\displaystyle 24\pi ^2\)

\(\displaystyle 24\pi\)

\(\displaystyle 144\pi\)

\(\displaystyle 144\)

Correct answer:

\(\displaystyle 144\pi\)

Explanation:

Write the formula for the area of a circle.

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

Substitute the radius.

\(\displaystyle A=\pi (12)^2 = \pi (144)\)

The answer is:  \(\displaystyle 144\pi\)

Example Question #135 : 2 Dimensional Geometry

Find the area of the circle with a circumference of \(\displaystyle 20\pi\).

Possible Answers:

\(\displaystyle 400\pi\)

\(\displaystyle 200\pi\)

\(\displaystyle 20\pi\)

\(\displaystyle 100\pi\)

\(\displaystyle 50\pi\)

Correct answer:

\(\displaystyle 100\pi\)

Explanation:

Write the formula for the circumference of a circle.

\(\displaystyle C = 2\pi r\)

Substitute the circumference into the equation.

\(\displaystyle 20\pi= 2\pi r\)

Divide both sides by \(\displaystyle 2\pi\).

\(\displaystyle \frac{20\pi}{2\pi}= \frac{2\pi r}{2\pi}\)

\(\displaystyle r=10\)

Write the formula for the area of a circle.

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

Substitute the radius into the equation.

\(\displaystyle A=\pi (10)^2 = 100\pi\)

The answer is:  \(\displaystyle 100\pi\)

Example Question #132 : 2 Dimensional Geometry

Find the area of a circle with a radius of \(\displaystyle 7\pi ^3\).

Possible Answers:

\(\displaystyle 7\pi ^6\)

\(\displaystyle 49 \pi ^6\)

\(\displaystyle 49 \pi ^7\)

\(\displaystyle 14\pi ^6\)

\(\displaystyle 14\pi ^7\)

Correct answer:

\(\displaystyle 49 \pi ^7\)

Explanation:

Write the formula for the area of a circle.

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

Substitute the radius into the formula.

\(\displaystyle A = \pi (7\pi ^3)^2 = \pi (7\pi ^3)(7\pi ^3)\)

The answer is:  \(\displaystyle 49 \pi ^7\)

Example Question #137 : 2 Dimensional Geometry

Find the area of a circle with a diameter of 18.

Possible Answers:

\(\displaystyle 108\pi\)

\(\displaystyle 18\pi\)

\(\displaystyle 162\pi\)

\(\displaystyle 81\pi\)

\(\displaystyle 324\pi\)

Correct answer:

\(\displaystyle 81\pi\)

Explanation:

Write the formula for the area of a circle.

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

The radius is half the diameter, or \(\displaystyle \frac{18}{2} = 9\).

Substitute the radius.

\(\displaystyle A = \pi (9)^2 = 81\pi\)

The answer is:  \(\displaystyle 81\pi\)

Example Question #138 : 2 Dimensional Geometry

Find the area of a circle with a radius of \(\displaystyle 2x+1\).

Possible Answers:

\(\displaystyle 4\pi x^2+4\pi x +\pi\)

\(\displaystyle 4x^2+4x +1\)

\(\displaystyle 4\pi x^2+1\)

\(\displaystyle 4\pi x^2+\pi\)

\(\displaystyle 4\pi x^2+4\pi x +1\)

Correct answer:

\(\displaystyle 4\pi x^2+4\pi x +\pi\)

Explanation:

Write the formula for the area of a circle.

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

Substitute the radius.

\(\displaystyle A =\pi (2x+1)^2 = (2x+1) (2x+1) \pi\)

Use the FOIL method to simplify the binomials.

\(\displaystyle (2x+1) (2x+1) = (2x)(2x) + (2x)(1) + (1)(2x)+(1)(1)\)

Simplify the terms.

\(\displaystyle 4x^2+2x+2x+1 = 4x^2+4x +1\)

Multiply this quantity by pi.

\(\displaystyle \pi (4x^2+4x +1)\)

The answer is:  \(\displaystyle 4\pi x^2+4\pi x +\pi\)

Example Question #139 : 2 Dimensional Geometry

Find the area of a circle with a radius of \(\displaystyle 3\pi ^8\).

Possible Answers:

\(\displaystyle 9\pi^{65}\)

\(\displaystyle 9\pi^{16}\)

\(\displaystyle \textup{The answer is not given.}\)

\(\displaystyle 9\pi^{64}\)

\(\displaystyle 9\pi^{17}\)

Correct answer:

\(\displaystyle 9\pi^{17}\)

Explanation:

Write the formula for the area of a circle.

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

Substitute the radius into the equation.

\(\displaystyle A= \pi (3\pi ^8)^2= \pi (3\pi ^8)(3\pi ^8)\)

The answer is:  \(\displaystyle 9\pi^{17}\)

Example Question #131 : Geometry And Graphs

Find the area of a circle with a radius of 25.

Possible Answers:

\(\displaystyle 525\pi\)

\(\displaystyle 50\pi\)

\(\displaystyle 625 \pi\)

\(\displaystyle 150\pi\)

\(\displaystyle 125\pi\)

Correct answer:

\(\displaystyle 625 \pi\)

Explanation:

Write the formula for the area of a circle.

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

Substitute the radius.

\(\displaystyle A=\pi (25)^2 = \pi (25)(25) = 625 \pi\)

The answer is:  \(\displaystyle 625 \pi\)

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