Intermediate Geometry : How to find the length of a chord

Study concepts, example questions & explanations for Intermediate Geometry

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Example Questions

Example Question #1 : Chords

The radius of \(\displaystyle \small \odot O\) is \(\displaystyle 6\) feet and \(\displaystyle \small m\widehat{AB}=60^{\circ}\).  Find the length of chord \(\displaystyle \small \overline{AB}\).

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Possible Answers:

\(\displaystyle \small 6\sqrt{2}\,ft.\)

\(\displaystyle \small 3\sqrt{3}\,ft.\)

\(\displaystyle \small 3\,ft.\)

\(\displaystyle \small 6 \,ft.\)

\(\displaystyle \small 8\,ft.\)

Correct answer:

\(\displaystyle \small 6 \,ft.\)

Explanation:

We begin by drawing in three radii:  one to \(\displaystyle \small A\), one to \(\displaystyle \small B\), and one perpendicular to \(\displaystyle \small \overline{AB}\) with endpoint \(\displaystyle \small C\) on our circle.

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We must also recall that our central angle \(\displaystyle \small \angle AOB\) has a measure equal to its intercepted arc.  Therefore, \(\displaystyle \small m\angle AOB=60^\circ\).  Our perpendicular radius actually divides \(\displaystyle \small \triangle AOB\) into two congruent triangles.  Therefore, it also bisects our central angle, meaning that \(\displaystyle \small m\angle AOC=m\angle COB=30^\circ\)

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Therefore, each of these triangles is a 30-60-90 triangle, meaning that each half of our chord is simply half the length of the hypotenuse (our radius which is 6).  Therefore, each half is 3, and the entire chord is 6 feet.

Example Question #134 : Intermediate Geometry

If a chord is \(\displaystyle 5\) units away from the center of a circle, and the radius is \(\displaystyle 7\), what is the length of that chord?

Possible Answers:

\(\displaystyle 4.5\)

\(\displaystyle 9.798\)

\(\displaystyle 10\)

\(\displaystyle 9\)

\(\displaystyle 9.234\)

Correct answer:

\(\displaystyle 9.798\)

Explanation:

Draw a segment perpendicular to the chord from the center, and this line will bisect the chord. Setting up the Pythagorean Theorem with the radius as the hypotenuse and the distance as one of the legs, we solve for the other leg.

\(\displaystyle 7^2-5^2=24\)  \(\displaystyle \rightarrow \sqrt{24}=4.8989\)

Since this leg is half of the chord, the total chord length is 2 times that, or 9.798.

\(\displaystyle 2(4.8989)=9.798\)

Example Question #1 : How To Find The Length Of A Chord

If a chord is \(\displaystyle 6\) units away from the center of a circle, and the radius is \(\displaystyle 10\), what is the length of that chord?

Possible Answers:

\(\displaystyle 16\)

\(\displaystyle 10\)

\(\displaystyle 17\)

\(\displaystyle 8\)

\(\displaystyle 12\)

Correct answer:

\(\displaystyle 16\)

Explanation:

Draw a segment perpendicular to the chord from the center, and this line will bisect the chord. Setting up the Pythagorean Theorem with the radius as the hypotenuse and the distance as one of the legs, we solve for the other leg.

\(\displaystyle 10^2-6^2=64 \rightarrow \sqrt{64}=8\)

Since this leg is half of the chord, the total chord length is 2 times that, or 16.

\(\displaystyle 2(8)=16\)

Example Question #136 : Intermediate Geometry

If a chord is \(\displaystyle 4.5\) units away from the center of a circle, and the radius is \(\displaystyle 6\), what is the length of that chord?

Possible Answers:

\(\displaystyle 7.7\)

\(\displaystyle 3.4\)

\(\displaystyle 11\)

\(\displaystyle 7.937\)

\(\displaystyle 3.963\)

Correct answer:

\(\displaystyle 7.937\)

Explanation:

Draw a segment perpendicular to the chord from the center, and this line will bisect the chord. Setting up the Pythagorean Theorem with the radius as the hypotenuse and the distance as one of the legs, we solve for the other leg.

\(\displaystyle 6^2-4.5^2=15.75 \rightarrow \sqrt{15.75}=3.9686\)

Since this leg is half of the chord, the total chord length is 2 times that, or 7.937.

\(\displaystyle 2(3.9686)=7.937\)

Example Question #1 : Chords

If a chord is \(\displaystyle 3\) units away from the center of a circle, and the radius is \(\displaystyle 3.5\), what is the length of that chord?

Possible Answers:

\(\displaystyle 7.212\)

\(\displaystyle 7\)

\(\displaystyle 11\)

\(\displaystyle 1.803\)

\(\displaystyle 3.606\)

Correct answer:

\(\displaystyle 3.606\)

Explanation:

Draw a segment perpendicular to the chord from the center, and this line will bisect the chord. Setting up the Pythagorean Theorem with the radius as the hypotenuse and the distance as one of the legs, we solve for the other leg.

\(\displaystyle 3.5^2-3^2=3.25 \rightarrow \sqrt{3.25}=1.8027\)

Since this leg is half of the chord, the total chord length is 2 times that, or 3.606.

\(\displaystyle 2(1.8027)=3.606\)

Example Question #1 : How To Find The Length Of A Chord

If a chord is \(\displaystyle 4\) units away from the center of a circle, and the radius is \(\displaystyle 5\), what is the length of that chord?

Possible Answers:

\(\displaystyle 3\)

\(\displaystyle 12\)

\(\displaystyle 9\)

\(\displaystyle 8\)

\(\displaystyle 6\)

Correct answer:

\(\displaystyle 6\)

Explanation:

Draw a segment perpendicular to the chord from the center, and this line will bisect the chord. Setting up the Pythagorean Theorem with the radius as the hypotenuse and the distance as one of the legs, we solve for the other leg.

\(\displaystyle 5^2-4^2=9 \rightarrow \sqrt{9}=3\)

Since this leg is half of the chord, the total chord length is 2 times that, or 6.

\(\displaystyle 2(3)=6\)

Example Question #139 : Intermediate Geometry

If a chord is \(\displaystyle 10\) units away from the center of a circle, and the radius is \(\displaystyle 12\), what is the length of that chord?

Possible Answers:

\(\displaystyle 12\)

\(\displaystyle 6.678\)

\(\displaystyle 11\)

\(\displaystyle 13.266\)

\(\displaystyle 26.44\)

Correct answer:

\(\displaystyle 13.266\)

Explanation:

Draw a segment perpendicular to the chord from the center, and this line will bisect the chord. Setting up the Pythagorean Theorem with the radius as the hypotenuse and the distance as one of the legs, we solve for the other leg.

\(\displaystyle 12^2-10^2=44 \rightarrow \sqrt{44}=6.6332\)

Since this leg is half of the chord, the total chord length is 2 times that, or 13.266.

\(\displaystyle 2(6.6332)=13.266\)

Example Question #2 : How To Find The Length Of A Chord

If a chord is \(\displaystyle 2\) units away from the center of a circle, and the radius is \(\displaystyle 3\), what is the length of that chord?

Possible Answers:

\(\displaystyle 10\)

\(\displaystyle 3\)

\(\displaystyle 8.908\)

\(\displaystyle 2.236\)

\(\displaystyle 4.472\)

Correct answer:

\(\displaystyle 4.472\)

Explanation:

Draw a segment perpendicular to the chord from the center, and this line will bisect the chord. Setting up the Pythagorean Theorem with the radius as the hypotenuse and the distance as one of the legs, we solve for the other leg.

\(\displaystyle 3^2-2^2=5 \rightarrow \sqrt{5}=2.2361\)

Since this leg is half of the chord, the total chord length is 2 times that, or 4.472.

\(\displaystyle 2(2.2361)=4.472\)

Example Question #1 : How To Find The Length Of A Chord

If a chord is \(\displaystyle 1\) units away from the center of a circle, and the radius is \(\displaystyle 4\), what is the length of that chord?

Possible Answers:

\(\displaystyle 7.746\)

\(\displaystyle 3.856\)

\(\displaystyle 4\)

\(\displaystyle 15.2\)

\(\displaystyle 11\)

Correct answer:

\(\displaystyle 7.746\)

Explanation:

Draw a segment perpendicular to the chord from the center, and this line will bisect the chord. Setting up the Pythagorean Theorem with the radius as the hypotenuse and the distance as one of the legs, we solve for the other leg.

\(\displaystyle 4^2-1^2=15 \rightarrow \sqrt{15}=3.873\)

Since this leg is half of the chord, the total chord length is 2 times that, or 7.746.

\(\displaystyle 2(3.873)=7.746\)

Example Question #142 : Circles

If a chord is \(\displaystyle 11\) units away from the center of a circle, and the radius is \(\displaystyle 12\), what is the length of that chord?

Possible Answers:

\(\displaystyle 4.75\)

\(\displaystyle 11\)

\(\displaystyle 12\)

\(\displaystyle 19.164\)

\(\displaystyle 9.592\)

Correct answer:

\(\displaystyle 9.592\)

Explanation:

Draw a segment perpendicular to the chord from the center, and this line will bisect the chord. Setting up the Pythagorean Theorem with the radius as the hypotenuse and the distance as one of the legs, we solve for the other leg.

\(\displaystyle 12^2-11^2=23 \rightarrow \sqrt{23}=4.7958\)

Since this leg is half of the chord, the total chord length is 2 times that, or 9.592.

\(\displaystyle 2(4.7958)=9.592\)

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