Common Core: High School - Geometry : Circles

Study concepts, example questions & explanations for Common Core: High School - Geometry

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Example Questions

Example Question #71 : Circles

Calculate the arc length of a circle that has a central angle of \displaystyle 93 degrees and an of \displaystyle 100.

Refer to the following figure to help calculate the solution.

Circlearc9 10

Possible Answers:

\displaystyle s=9.185

\displaystyle s=9.851

\displaystyle s=9.158

\displaystyle s=9.518

\displaystyle s=9.150

Correct answer:

\displaystyle s=9.158

Explanation:

To calculate the arc length of a circle that has a central angle of \displaystyle 93 degrees and a circumference of \displaystyle 100, refer to the figure and the algebraic formula for arc length.

 Circlearc9 10

The algebraic formula for arc length is as follows.

\displaystyle s=\frac{\theta}{360^\circ}\times C

where,

\displaystyle \\s=\text{Arc Length} \\C=\text{Circumference} \\\theta=\text{Central Angle}\\A=Area

For this particular question the known information is,

\displaystyle \\s=\text{Arc Length} \\A=100 \\\theta=93^\circ\\A=\pi r^2\\C=2\pi r

First, calculate the radius and the circumference.

\displaystyle \\100=\pi r^2 \\\\\frac{100}{\pi}=r^2 \\\\\sqrt{\frac{100}{\pi}}=r

\displaystyle C=2\pi\sqrt{\frac{100}{\pi}}

Substitute these values into the formula and solve for the arc length.

\displaystyle s=\frac{\theta}{360^\circ}\times C

\displaystyle s=\frac{93^\circ}{360^\circ}\times 2\pi\sqrt{\frac{100}{\pi}}

\displaystyle s=9.158

Example Question #23 : Arc Length, Radii, Radian, And Sector Similarity And Proportionality: Ccss.Math.Content.Hsg C.B.5

Calculate the arc length of a circle that has a central angle of \displaystyle 58 degrees and an of \displaystyle 15.

Refer to the following figure to help calculate the solution.

Circlearc11 12

Possible Answers:

\displaystyle s=2.212

\displaystyle s=2.122

\displaystyle s=2.207

\displaystyle s=2.218

\displaystyle s=2.221

Correct answer:

\displaystyle s=2.212

Explanation:

To calculate the arc length of a circle that has a central angle of \displaystyle 58 degrees and a circumference of \displaystyle 15, refer to the figure and the algebraic formula for arc length.

 Circlearc11 12

The algebraic formula for arc length is as follows.

\displaystyle s=\frac{\theta}{360^\circ}\times C

where,

\displaystyle \\s=\text{Arc Length} \\C=\text{Circumference} \\\theta=\text{Central Angle}\\A=Area

For this particular question the known information is,

\displaystyle \\s=\text{Arc Length} \\A=15 \\\theta=58^\circ\\A=\pi r^2\\C=2\pi r

First, calculate the radius and the circumference.

\displaystyle \\15=\pi r^2 \\\\\frac{15}{\pi}=r^2 \\\\\sqrt{\frac{15}{\pi}}=r

\displaystyle C=2\pi\sqrt{\frac{15}{\pi}}

Substitute these values into the formula and solve for the arc length.

\displaystyle s=\frac{\theta}{360^\circ}\times C

\displaystyle s=\frac{58^\circ}{360^\circ}\times 2\pi\sqrt{\frac{15}{\pi}}

\displaystyle s=2.212

Example Question #71 : Circles

Determine the area of the sector of a circle that has a central angle of \displaystyle 58 degrees and an area of \displaystyle 15.

Refer to the following figure to help calculate the solution.

Circlearc11 12

Possible Answers:

\displaystyle \text{sector area}= 2.61\overline{4}

\displaystyle \text{sector area}= 2.46\overline{1}

\displaystyle \text{sector area}= 2.41\overline{6}

\displaystyle \text{sector area}= 2.14\overline{6}

\displaystyle \text{sector area}= 2.41\overline{9}

Correct answer:

\displaystyle \text{sector area}= 2.41\overline{6}

Explanation:

State the known information,

\displaystyle \\\text{Circle Area}= 15 \\\text{Central Angle}=58^\circ

Since the question is asking for the area of the sector, a ratio will need to be constructed. Recall that a circle is composed of 360 degrees. Therefore, the following ratio can be made,

\displaystyle \\\frac{\theta}{360^\circ}=\frac{\text{sector area}}{15} \\\\\frac{58^\circ}{360^\circ}=\frac{\text{sector area}}{15} \\\\\frac{29}{180}=\frac{\text{sector area}}{15} \\\\\frac{29}{180}\times 15=\text{sector area} \\\\\text{sector area}=2.41\overline{6}

All Common Core: High School - Geometry Resources

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