Basic Geometry : How to find circumference

Study concepts, example questions & explanations for Basic Geometry

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Example Questions

Example Question #251 : Radius

The rectangle and the circle share the same center, \displaystyle C. Find the circumference of the circle.

11

Possible Answers:

\displaystyle 4\sqrt{10}\pi

\displaystyle 6\sqrt{10}\pi

\displaystyle 3\sqrt{10}\pi

\displaystyle 5\sqrt{10}\pi

Correct answer:

\displaystyle 4\sqrt{10}\pi

Explanation:

13

Notice that the diagonal of the rectangle is also the diameter of the circle. 

Use the Pythagorean theorem to find the length of the diagonal.

\displaystyle \text{length}^2+\text{width}^2=\text{diagonal}^2

\displaystyle \text{diagonal}=\sqrt{\text{length}^2+\text{width}^2}

Substitute in the values of the length and the width to find the length of the diagonal.

\displaystyle \text{diagonal}=\sqrt{4^2+12^2}

Simplify.

\displaystyle \text{diagonal}=\sqrt{160}

Reduce.

\displaystyle \text{diagonal}=4\sqrt{10}

Now, recall the relationship between the diagonal and the diameter.

\displaystyle \text{diagonal}=\text{diameter}=4\sqrt{10}

Recall how to find the circumference of a circle:

\displaystyle \text{Circumference}=\text{diameter}\times\pi

Substitute in the value of the diameter to find the circumference.

\displaystyle \text{Circumference}=4\sqrt{10}\pi

Example Question #252 : Plane Geometry

The rectangle and the circle share the same center, \displaystyle C. Find the circumference of the circle.

12

Possible Answers:

\displaystyle 4\sqrt{19}\pi

\displaystyle 4\sqrt{17}\pi

\displaystyle 4\sqrt{15}\pi

\displaystyle 4\sqrt{14}\pi

Correct answer:

\displaystyle 4\sqrt{17}\pi

Explanation:

13

Notice that the diagonal of the rectangle is also the diameter of the circle. 

Use the Pythagorean theorem to find the length of the diagonal.

\displaystyle \text{length}^2+\text{width}^2=\text{diagonal}^2

\displaystyle \text{diagonal}=\sqrt{\text{length}^2+\text{width}^2}

Substitute in the values of the length and the width to find the length of the diagonal.

\displaystyle \text{diagonal}=\sqrt{4^2+16^2}

Simplify.

\displaystyle \text{diagonal}=\sqrt{272}

Reduce.

\displaystyle \text{diagonal}=4\sqrt{17}

Now, recall the relationship between the diagonal and the diameter.

\displaystyle \text{diagonal}=\text{diameter}=4\sqrt{17}

Recall how to find the circumference of a circle:

\displaystyle \text{Circumference}=\text{diameter}\times\pi

Substitute in the value of the diameter to find the circumference.

\displaystyle \text{Circumference}=4\sqrt{17}\pi

Example Question #61 : How To Find Circumference

Find the circumference of a circle given radius \displaystyle 4x.

Possible Answers:

\displaystyle 8x\pi

\displaystyle 4x

\displaystyle 8x

\displaystyle 4x\pi

Correct answer:

\displaystyle 8x\pi

Explanation:

To solve, simply use the formula for circumference. Thus,

\displaystyle C=2\pi{r}=2*\pi*4x=8x\pi

Example Question #62 : How To Find Circumference

If a rectangle with a diagonal of \displaystyle 14\sqrt7 is inscribed in a circle, what is the circumference of the circle?

Possible Answers:

\displaystyle 28\sqrt7\pi

\displaystyle 196\pi

\displaystyle 32\pi

\displaystyle 14\sqrt7\pi

Correct answer:

\displaystyle 14\sqrt7\pi

Explanation:

13

Notice that the diagonal of the rectangle is the same as the diameter of the circle.

\displaystyle \text{Diameter}=\text{Diagonal}=14\sqrt7

Now, recall how to find the circumference of a circle.

\displaystyle \text{Circumference}=\text{diameter}\times\pi

Substitute in the given diameter to find the circumference.

\displaystyle \text{Circumference}=14\sqrt7\pi

Example Question #63 : How To Find Circumference

If a rectangle with a diagonal of \displaystyle 12 is inscribed in a circle, what is the circumference of the circle?

Possible Answers:

\displaystyle 6\pi

\displaystyle 144\pi

\displaystyle 12\pi

\displaystyle 4\pi

Correct answer:

\displaystyle 12\pi

Explanation:

13

Notice that the diagonal of the rectangle is the same as the diameter of the circle.

\displaystyle \text{Diameter}=\text{Diagonal}=12

Now, recall how to find the circumference of a circle.

\displaystyle \text{Circumference}=\text{diameter}\times\pi

Substitute in the given diameter to find the circumference.

\displaystyle \text{Circumference}=12\pi

Example Question #62 : How To Find Circumference

If a rectangle with a diagonal of \displaystyle 2\sqrt5 is inscribed in a circle, what is the circumference of the circle?

Possible Answers:

\displaystyle 4\sqrt{5}\pi

\displaystyle 8\sqrt5\pi

\displaystyle 50\pi

\displaystyle 2\sqrt5\pi

Correct answer:

\displaystyle 2\sqrt5\pi

Explanation:

13

Notice that the diagonal of the rectangle is the same as the diameter of the circle.

\displaystyle \text{Diameter}=\text{Diagonal}=2\sqrt5

Now, recall how to find the circumference of a circle.

\displaystyle \text{Circumference}=\text{diameter}\times\pi

Substitute in the given diameter to find the circumference.

\displaystyle \text{Circumference}=2\sqrt5\pi

Example Question #65 : How To Find Circumference

If a rectangle with a diagonal of \displaystyle 4\sqrt{10} is inscribed in a circle, what is the circumference of the circle?

Possible Answers:

\displaystyle 4\sqrt{10}\pi

\displaystyle 160\pi

\displaystyle 80\pi

\displaystyle 8\sqrt{10}\pi

Correct answer:

\displaystyle 4\sqrt{10}\pi

Explanation:

13

Notice that the diagonal of the rectangle is the same as the diameter of the circle.

\displaystyle \text{Diameter}=\text{Diagonal}=4\sqrt{10}

Now, recall how to find the circumference of a circle.

\displaystyle \text{Circumference}=\text{diameter}\times\pi

Substitute in the given diameter to find the circumference.

\displaystyle \text{Circumference}=4\sqrt{10}\pi

Example Question #252 : Basic Geometry

If a rectangle with a diagonal of \displaystyle 15\sqrt3 is inscribed in a circle, what is the circumference of the circle?

Possible Answers:

\displaystyle 30\sqrt3\pi

\displaystyle 250\pi

\displaystyle 15\sqrt3\pi

\displaystyle 15\pi

Correct answer:

\displaystyle 15\sqrt3\pi

Explanation:

13

Notice that the diagonal of the rectangle is the same as the diameter of the circle.

\displaystyle \text{Diameter}=\text{Diagonal}=15\sqrt3

Now, recall how to find the circumference of a circle.

\displaystyle \text{Circumference}=\text{diameter}\times\pi

Substitute in the given diameter to find the circumference.

\displaystyle \text{Circumference}=15\sqrt3\pi 

Example Question #62 : How To Find Circumference

If a rectangle with a diagonal of \displaystyle 224 is inscribed in a circle, what is the circumference of the circle?

Possible Answers:

\displaystyle 112\pi

\displaystyle 24\sqrt{3}\pi

\displaystyle 336\pi

\displaystyle 224\pi

Correct answer:

\displaystyle 224\pi

Explanation:

13

Notice that the diagonal of the rectangle is the same as the diameter of the circle.

\displaystyle \text{Diameter}=\text{Diagonal}=224

Now, recall how to find the circumference of a circle.

\displaystyle \text{Circumference}=\text{diameter}\times\pi

Substitute in the given diameter to find the circumference.

\displaystyle \text{Circumference}=224\pi

Example Question #261 : Basic Geometry

If a rectangle with a diagonal of \displaystyle 19 is inscribed in a circle, what is the circumference of the circle?

Possible Answers:

\displaystyle 19\pi

\displaystyle 381\pi

\displaystyle 38\pi

\displaystyle \frac{19}{2}\pi

Correct answer:

\displaystyle 19\pi

Explanation:

13

Notice that the diagonal of the rectangle is the same as the diameter of the circle.

\displaystyle \text{Diameter}=\text{Diagonal}=19

Now, recall how to find the circumference of a circle.

\displaystyle \text{Circumference}=\text{diameter}\times\pi

Substitute in the given diameter to find the circumference.

\displaystyle \text{Circumference}=19\pi

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