Basic Geometry : Radius

Study concepts, example questions & explanations for Basic Geometry

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Example Questions

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.

\(\displaystyle \text{Circumference}=19\pi\)

Example Question #261 : Radius

If a rectangle with a diagonal of \(\displaystyle \frac{4}{5}\) is inscribed in a circle, what is the circumference of the circle?

Possible Answers:

\(\displaystyle \frac{4}{5}\pi\)

\(\displaystyle \frac{5}{4}\pi\)

\(\displaystyle \frac{2\sqrt5}{5}\pi\)

\(\displaystyle \frac{16}{25}\pi\)

Correct answer:

\(\displaystyle \frac{4}{5}\pi\)

Explanation:

13

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

\(\displaystyle \text{Diameter}=\text{Diagonal}=\frac{4}{5}\)

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.

\(\displaystyle \text{Circumference}=\frac{4}{5}\pi\)

Example Question #263 : Basic Geometry

If a rectangle with a diagonal of \(\displaystyle 4\sqrt3\) is inscribed in a circle, what is the circumference of the circle?

Possible Answers:

\(\displaystyle 16\sqrt3\pi\)

\(\displaystyle 4\sqrt3\pi\)

\(\displaystyle 8\sqrt3\pi\)

\(\displaystyle 6\pi\)

Correct answer:

\(\displaystyle 4\sqrt3\pi\)

Explanation:

13

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

\(\displaystyle \text{Diameter}=\text{Diagonal}=4\sqrt3\)

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.

\(\displaystyle \text{Circumference}=4\sqrt3\pi\)

Example Question #264 : Basic Geometry

If a rectangle with a diagonal of \(\displaystyle 201\) is inscribed in a circle, what is the circumference of the circle?

Possible Answers:

\(\displaystyle 402\pi\)

\(\displaystyle 201\pi\)

\(\displaystyle \frac{201}{2}\pi\)

\(\displaystyle 201\)

Correct answer:

\(\displaystyle 201\pi\)

Explanation:

13

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

\(\displaystyle \text{Diameter}=\text{Diagonal}=201\)

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.

\(\displaystyle \text{Circumference}=201\pi\)

Example Question #261 : Basic Geometry

If a rectangle with a diagonal of \(\displaystyle 18\sqrt{7}\) is inscribed in a circle, what is the circumference of the circle?

Possible Answers:

\(\displaystyle 12\sqrt7\pi\)

\(\displaystyle 9\sqrt7\pi\)

\(\displaystyle 36\sqrt7\pi\)

\(\displaystyle 18\sqrt7\pi\)

Correct answer:

\(\displaystyle 18\sqrt7\pi\)

Explanation:

13

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

\(\displaystyle \text{Diameter}=\text{Diagonal}=18\sqrt7\)

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.

\(\displaystyle \text{Circumference}=18\sqrt7\pi\)

Example Question #266 : Basic Geometry

If a rectangle with a diagonal of \(\displaystyle \frac{9}{8}\) is inscribed in a circle, what is the circumference of the circle?

Possible Answers:

\(\displaystyle \frac{4}{3}\pi\)

\(\displaystyle \frac{9}{8}\pi\)

\(\displaystyle 3\sqrt2\pi\)

\(\displaystyle \frac{8}{9}\pi\)

Correct answer:

\(\displaystyle \frac{9}{8}\pi\)

Explanation:

13

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

\(\displaystyle \text{Diameter}=\text{Diagonal}=\frac{8}{9}\)

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.

\(\displaystyle \text{Circumference}=\frac{8}{9}\pi\)

Example Question #261 : Circles

Given that the radius of a circle is \(\displaystyle 20m\), solve for the circumference. 

Possible Answers:

\(\displaystyle 72.6 m\)

\(\displaystyle 103.5 m\)

\(\displaystyle 125.7 m\)

\(\displaystyle 123.4 m\)

\(\displaystyle 40 m\)

Correct answer:

\(\displaystyle 125.7 m\)

Explanation:

The circumference of a circle is found by using the following formula:

\(\displaystyle C=2 (\pi) (r)\)Plug in the radius from the given information, and you get this:

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

\(\displaystyle C = 125.7 m\)

Example Question #262 : Basic Geometry

Find the circumference of a circle given the radius is 3.

Possible Answers:

\(\displaystyle 9\pi\)

\(\displaystyle 12\pi\)

\(\displaystyle 6\pi\)

\(\displaystyle 18\pi\)

Correct answer:

\(\displaystyle 6\pi\)

Explanation:

To solve, simply use the formula for the circumference of a circle.

Given that the radius is 3, substitute 3 in for the r in the circumference formula below.

Thus,

\(\displaystyle \\C=2\pi{r}\\C=2*\pi*3\\C=6\pi\).

Example Question #269 : Basic Geometry

Find the circumference of the circle if the lengths of the legs of the inscribed isosceles triangle are \(\displaystyle 2\sqrt2\).

1

Possible Answers:

\(\displaystyle 8\pi\)

\(\displaystyle 4\pi\)

\(\displaystyle 12\pi\)

\(\displaystyle 16\pi\)

Correct answer:

\(\displaystyle 4\pi\)

Explanation:

1

Notice that the hypotenuse of the triangle in the figure is also the diameter of the circle.

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

\(\displaystyle \text{Hypotenuse}^2=\text{leg}^2+\text{leg}^2\)

\(\displaystyle \text{Hypotenuse}^2=2(\text{leg}^2)\)

\(\displaystyle \text{Hypotenuse}=\sqrt{2(\text{leg}^2)}=\text{leg}\sqrt2\)

Substitute in the length of triangle’s legs to find the missing length of the hypotenuse.

\(\displaystyle \text{Hypotenuse}=2\sqrt2(\sqrt2)\)

Simplify.

\(\displaystyle \text{Hypotenuse}=4\)

Now, recall that the hypotenuse of the triangle and the diameter of the circle are the same:

\(\displaystyle \text{Hypotenuse}=\text{Diameter}=4\)

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

\(\displaystyle \text{Circumference}=\text{Diameter}\times\pi\)

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

\(\displaystyle \text{Circumference}=4\pi\)

Example Question #270 : Basic Geometry

Find the circumference of the circle if the lengths of the legs of the inscribed isosceles triangle are \(\displaystyle 3\sqrt2\).

1

Possible Answers:

\(\displaystyle 6\pi\)

\(\displaystyle 12\pi\)

\(\displaystyle 18\pi\)

\(\displaystyle 3\pi\)

Correct answer:

\(\displaystyle 6\pi\)

Explanation:

1

Notice that the hypotenuse of the triangle in the figure is also the diameter of the circle.

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

\(\displaystyle \text{Hypotenuse}^2=\text{leg}^2+\text{leg}^2\)

\(\displaystyle \text{Hypotenuse}^2=2(\text{leg}^2)\)

\(\displaystyle \text{Hypotenuse}=\sqrt{2(\text{leg}^2)}=\text{leg}\sqrt2\)

Substitute in the length of triangle’s legs to find the missing length of the hypotenuse.

\(\displaystyle \text{Hypotenuse}=3\sqrt2(\sqrt2)\)

Simplify.

\(\displaystyle \text{Hypotenuse}=6\)

Now, recall that the hypotenuse of the triangle and the diameter of the circle are the same:

\(\displaystyle \text{Hypotenuse}=\text{Diameter}=6\)

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

\(\displaystyle \text{Circumference}=\text{Diameter}\times\pi\)

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

\(\displaystyle \text{Circumference}=6\pi\)

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