Intermediate Geometry : Sectors

Study concepts, example questions & explanations for Intermediate Geometry

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Example Questions

Example Question #121 : Plane Geometry

A sector in a circle with a radius of \(\displaystyle 9\) has an area of \(\displaystyle 16\pi\). In degrees, what is the measurement of the central angle of the circle?

Possible Answers:

\(\displaystyle 74.11^\circ\)

\(\displaystyle 81.11^\circ\)

\(\displaystyle 71.11^\circ\)

\(\displaystyle 72.11^\circ\)

Correct answer:

\(\displaystyle 71.11^\circ\)

Explanation:

Recall how to find the area of a sector:

\(\displaystyle \text{Area of Sector}=\frac{\text{Measurement of Central Angle}}{360}\times\pi\times r^2\)

Since the question asks for the measurement of the central angle, rearrange the equation like thus:

\(\displaystyle \text{Measurement of Central Angle}=\frac{360\times\text{Area of Sector}}{\pi\times r^2}\)

Plug in the given information to find the measurement of the central angle.

\(\displaystyle \text{Measurement of Central Angle}=\frac{360\times 16\pi}{\pi\times 9^2}=\frac{5760\pi}{81\pi}=71.11\)

The central angle is \(\displaystyle 71.11\) degrees.

Make sure to round to \(\displaystyle 2\) places after the decimal.

Example Question #122 : Plane Geometry

A sector in a circle with a radius of \(\displaystyle 9\) has an area of \(\displaystyle 9\pi\). In degrees, what is the measurement of the central angle of the sector?

Possible Answers:

\(\displaystyle 40^\circ\)

\(\displaystyle 25^\circ\)

\(\displaystyle 35^\circ\)

\(\displaystyle 30^\circ\)

Correct answer:

\(\displaystyle 40^\circ\)

Explanation:

Recall how to find the area of a sector:

\(\displaystyle \text{Area of Sector}=\frac{\text{Measurement of Central Angle}}{360}\times\pi\times r^2\)

Since the question asks for the measurement of the central angle, rearrange the equation like thus:

\(\displaystyle \text{Measurement of Central Angle}=\frac{360\times\text{Area of Sector}}{\pi\times r^2}\)

Plug in the given information to find the measurement of the central angle.

\(\displaystyle \text{Measurement of Central Angle}=\frac{360\times 9\pi}{\pi\times 9^2}=\frac{3240\pi}{81\pi}=40\)

The central angle is \(\displaystyle 40\) degrees.

Example Question #123 : Plane Geometry

A sector in a circle with a radius of \(\displaystyle 9\) has an area of \(\displaystyle 2\pi\). In degrees, what is the measurement of the central angle of the sector?

Possible Answers:

\(\displaystyle 12.89^\circ\)

\(\displaystyle 6.89^\circ\)

\(\displaystyle 10.89^\circ\)

\(\displaystyle 8.89^\circ\)

Correct answer:

\(\displaystyle 8.89^\circ\)

Explanation:

Recall how to find the area of a sector:

\(\displaystyle \text{Area of Sector}=\frac{\text{Measurement of Central Angle}}{360}\times\pi\times r^2\)

Since the question asks for the measurement of the central angle, rearrange the equation like thus:

\(\displaystyle \text{Measurement of Central Angle}=\frac{360\times\text{Area of Sector}}{\pi\times r^2}\)

Plug in the given information to find the measurement of the central angle.

\(\displaystyle \text{Measurement of Central Angle}=\frac{360\times 2\pi}{\pi\times 9^2}=\frac{720\pi}{81\pi}=8.89\)

The central angle is \(\displaystyle 8.89\) degrees.

Make sure to round to \(\displaystyle 2\) places after the decimal.

Example Question #124 : Plane Geometry

A sector in a circle with a radius of \(\displaystyle 9\) has an area of \(\displaystyle 3\pi\). In degrees, what is the measurement of the central angle of the sector?

Possible Answers:

\(\displaystyle 16.33^\circ\)

\(\displaystyle 13.33^\circ\)

\(\displaystyle 10.33^\circ\)

\(\displaystyle 9.33^\circ\)

Correct answer:

\(\displaystyle 13.33^\circ\)

Explanation:

Recall how to find the area of a sector:

\(\displaystyle \text{Area of Sector}=\frac{\text{Measurement of Central Angle}}{360}\times\pi\times r^2\)

Since the question asks for the measurement of the central angle, rearrange the equation like thus:

\(\displaystyle \text{Measurement of Central Angle}=\frac{360\times\text{Area of Sector}}{\pi\times r^2}\)

Plug in the given information to find the measurement of the central angle.

\(\displaystyle \text{Measurement of Central Angle}=\frac{360\times 3\pi}{\pi\times 9^2}=\frac{1080\pi}{81\pi}=13.33\)

The central angle is \(\displaystyle 13.33\) degrees.

Make sure to round to \(\displaystyle 2\) places after the decimal.

Example Question #125 : Plane Geometry

A sector in a circle with a radius of \(\displaystyle 12\) has an area of \(\displaystyle 12\pi\). In degrees, what is the measurement of the central angle of the sector?

Possible Answers:

\(\displaystyle 30^\circ\)

\(\displaystyle 60^\circ\)

\(\displaystyle 40^\circ\)

\(\displaystyle 15^\circ\)

Correct answer:

\(\displaystyle 30^\circ\)

Explanation:

Recall how to find the area of a sector:

\(\displaystyle \text{Area of Sector}=\frac{\text{Measurement of Central Angle}}{360}\times\pi\times r^2\)

Since the question asks for the measurement of the central angle, rearrange the equation like thus:

\(\displaystyle \text{Measurement of Central Angle}=\frac{360\times\text{Area of Sector}}{\pi\times r^2}\)

Plug in the given information to find the measurement of the central angle.

\(\displaystyle \text{Measurement of Central Angle}=\frac{360\times 12\pi}{\pi\times 12^2}=\frac{4320\pi}{144\pi}=30\)

The central angle is \(\displaystyle 30\) degrees.

Example Question #126 : Plane Geometry

A sector in a circle with a radius of \(\displaystyle 12\) has an area of \(\displaystyle 100\pi\). In degrees, what is the measurement of the central angle of the sector?

Possible Answers:

\(\displaystyle 250^\circ\)

\(\displaystyle 190^\circ\)

\(\displaystyle 220^\circ\)

\(\displaystyle 160^\circ\)

Correct answer:

\(\displaystyle 250^\circ\)

Explanation:

Recall how to find the area of a sector:

\(\displaystyle \text{Area of Sector}=\frac{\text{Measurement of Central Angle}}{360}\times\pi\times r^2\)

Since the question asks for the measurement of the central angle, rearrange the equation like thus:

\(\displaystyle \text{Measurement of Central Angle}=\frac{360\times\text{Area of Sector}}{\pi\times r^2}\)

Plug in the given information to find the measurement of the central angle.

\(\displaystyle \text{Measurement of Central Angle}=\frac{360\times 100\pi}{\pi\times 12^2}=\frac{36000\pi}{144\pi}=250\)

The central angle is \(\displaystyle 250\) degrees.

Example Question #127 : Plane Geometry

A sector in a circle with a radius of \(\displaystyle 12\) has an area of \(\displaystyle 120\pi\). In degrees, what is the measurement of the central angle of the sector?

Possible Answers:

\(\displaystyle 280^\circ\)

\(\displaystyle 250^\circ\)

\(\displaystyle 320^\circ\)

\(\displaystyle 300^\circ\)

Correct answer:

\(\displaystyle 300^\circ\)

Explanation:

Recall how to find the area of a sector:

\(\displaystyle \text{Area of Sector}=\frac{\text{Measurement of Central Angle}}{360}\times\pi\times r^2\)

Since the question asks for the measurement of the central angle, rearrange the equation like thus:

\(\displaystyle \text{Measurement of Central Angle}=\frac{360\times\text{Area of Sector}}{\pi\times r^2}\)

Plug in the given information to find the measurement of the central angle.

\(\displaystyle \text{Measurement of Central Angle}=\frac{360\times 120\pi}{\pi\times 12^2}=\frac{43200\pi}{144\pi}=300\)

The central angle is \(\displaystyle 300\) degrees.

Example Question #128 : Plane Geometry

A sector in a circle with a radius of \(\displaystyle 12\) has an area of \(\displaystyle 45\pi\). In degrees, what is the measurement of the central angle of the sector?

Possible Answers:

\(\displaystyle 118.5^\circ\)

\(\displaystyle 106.5^\circ\)

\(\displaystyle 112.5^\circ\)

\(\displaystyle 100.5^\circ\)

Correct answer:

\(\displaystyle 112.5^\circ\)

Explanation:

Recall how to find the area of a sector:

\(\displaystyle \text{Area of Sector}=\frac{\text{Measurement of Central Angle}}{360}\times\pi\times r^2\)

Since the question asks for the measurement of the central angle, rearrange the equation like thus:

\(\displaystyle \text{Measurement of Central Angle}=\frac{360\times\text{Area of Sector}}{\pi\times r^2}\)

Plug in the given information to find the measurement of the central angle.

\(\displaystyle \text{Measurement of Central Angle}=\frac{360\times 45\pi}{\pi\times 12^2}=\frac{16200\pi}{144\pi}=112.5\)

The central angle is \(\displaystyle 112.5\) degrees.

Example Question #21 : How To Find The Angle Of A Sector

Circle z

Refer to the above figure.

True, false, or undetermined: \(\displaystyle \angle AWB\) is a right angle.

Possible Answers:

Undetermined

True

False

Correct answer:

True

Explanation:

\(\displaystyle \angle AVB\) and \(\displaystyle \angle AWB\), being inscribed angles of the same circle which intercept the same arc, are congruent angles. \(\displaystyle \angle AVB\) is right, so \(\displaystyle \angle AWB\) must also be right.

Example Question #122 : Sectors

True or false: A \(\displaystyle 45^{\circ }\) sector of a circle comprises one eighth of the circle.

Possible Answers:

False

True

Correct answer:

True

Explanation:

A circle includes \(\displaystyle 360^{\circ }\) of angle measure, so a sector of measure \(\displaystyle N^{\circ }\) is \(\displaystyle \frac{N}{360}\) of the circle. Set \(\displaystyle N = 45\) - the sector is 

\(\displaystyle \frac{45}{360} = \frac{1}{8}\)

of the circle. The statement is true.

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