Basic Geometry : How to find circumference

Study concepts, example questions & explanations for Basic Geometry

varsity tutors app store varsity tutors android store

Example Questions

Example Question #81 : How To Find Circumference

Find the circumference of the circle if the lengths of the legs of the inscribed isosceles triangle are \(\displaystyle 5\sqrt2\).

1

Possible Answers:

\(\displaystyle 20\pi\)

\(\displaystyle 30\pi\)

\(\displaystyle 25\pi\)

\(\displaystyle 10\pi\)

Correct answer:

\(\displaystyle 10\pi\)

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.

\(\displaystyle \text{Hypotenuse}=5\sqrt2(\sqrt2)\)

Simplify.

\(\displaystyle \text{Hypotenuse}=10\)

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

\(\displaystyle \text{Hypotenuse}=\text{Diameter}=10\)

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.

\(\displaystyle \text{Circumference}=10\pi\)

Example Question #271 : Radius

Find the circumference of the circle if the lengths of the legs of the inscribed isosceles triangle are \(\displaystyle 6\sqrt2\).

1

Possible Answers:

\(\displaystyle 24\pi\)

\(\displaystyle 144\)

\(\displaystyle 18\pi\)

\(\displaystyle 12\pi\)

Correct answer:

\(\displaystyle 12\pi\)

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.

\(\displaystyle \text{Hypotenuse}=6\sqrt2(\sqrt2)\)

Simplify.

\(\displaystyle \text{Hypotenuse}=12\)

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

\(\displaystyle \text{Hypotenuse}=\text{Diameter}=12\)

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.

\(\displaystyle \text{Circumference}=12\pi\)

Example Question #81 : How To Find Circumference

Find the circumference of the circle if the lengths of the legs of the inscribed isosceles triangle are \(\displaystyle 7\sqrt2\).

1

Possible Answers:

\(\displaystyle 35\pi\)

\(\displaystyle 49\)

\(\displaystyle 28\pi\)

\(\displaystyle 14\pi\)

Correct answer:

\(\displaystyle 14\pi\)

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.

\(\displaystyle \text{Hypotenuse}=7\sqrt2(\sqrt2)\)

Simplify.

\(\displaystyle \text{Hypotenuse}=14\)

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

\(\displaystyle \text{Hypotenuse}=\text{Diameter}=14\)

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.

\(\displaystyle \text{Circumference}=14\pi\)

Example Question #273 : Radius

Find the circumference of the circle if the lengths of the legs of the inscribed isosceles triangle are \(\displaystyle 9\sqrt2\).

1

Possible Answers:

\(\displaystyle 81\)

\(\displaystyle 54\pi\)

\(\displaystyle 36\pi\)

\(\displaystyle 18\pi\)

Correct answer:

\(\displaystyle 18\pi\)

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.

\(\displaystyle \text{Hypotenuse}=9\sqrt2(\sqrt2)\)

Simplify.

\(\displaystyle \text{Hypotenuse}=18\)

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

\(\displaystyle \text{Hypotenuse}=\text{Diameter}=18\)

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.

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

Example Question #274 : Radius

Find the circumference of the circle if the lengths of the legs of the inscribed isosceles triangle are \(\displaystyle 8\sqrt2\).

1

Possible Answers:

\(\displaystyle 96\pi\)

\(\displaystyle 16\pi\)

\(\displaystyle 32\pi\)

\(\displaystyle 64\pi\)

Correct answer:

\(\displaystyle 16\pi\)

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.

\(\displaystyle \text{Hypotenuse}=8\sqrt2(\sqrt2)\)

Simplify.

\(\displaystyle \text{Hypotenuse}=16\)

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

\(\displaystyle \text{Hypotenuse}=\text{Diameter}=16\)

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.

\(\displaystyle \text{Circumference}=16\pi\)

Example Question #82 : How To Find Circumference

Find the circumference of the circle if the lengths of the legs of the inscribed isosceles triangle are \(\displaystyle 10\sqrt2\).

1

Possible Answers:

\(\displaystyle 40\pi\)

\(\displaystyle 80\pi\)

\(\displaystyle 160\pi\)

\(\displaystyle 20\pi\)

Correct answer:

\(\displaystyle 20\pi\)

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.

\(\displaystyle \text{Hypotenuse}=10\sqrt2(\sqrt2)\)

Simplify.

\(\displaystyle \text{Hypotenuse}=20\)

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

\(\displaystyle \text{Hypotenuse}=\text{Diameter}=20\)

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.

\(\displaystyle \text{Circumference}=20\pi\)

Example Question #275 : Radius

Find the circumference of the circle if the lengths of the legs of the inscribed isosceles triangle are \(\displaystyle 11\sqrt2\).

1

Possible Answers:

\(\displaystyle 44\pi\)

\(\displaystyle 121\)

\(\displaystyle 22\pi\)

\(\displaystyle 66\pi\)

Correct answer:

\(\displaystyle 22\pi\)

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.

\(\displaystyle \text{Hypotenuse}=11\sqrt2(\sqrt2)\)

Simplify.

\(\displaystyle \text{Hypotenuse}=22\)

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

\(\displaystyle \text{Hypotenuse}=\text{Diameter}=22\)

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.

\(\displaystyle \text{Circumference}=22\pi\)

Example Question #276 : Radius

Find the circumference of the circle if the lengths of the legs of the inscribed isosceles triangle are \(\displaystyle 12\sqrt2\).

1

Possible Answers:

\(\displaystyle 36\)

\(\displaystyle 24\pi\)

\(\displaystyle 48\pi\)

\(\displaystyle 12\pi\)

Correct answer:

\(\displaystyle 24\pi\)

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.

\(\displaystyle \text{Hypotenuse}=12\sqrt2(\sqrt2)\)

Simplify.

\(\displaystyle \text{Hypotenuse}=24\)

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

\(\displaystyle \text{Hypotenuse}=\text{Diameter}=24\)

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.

\(\displaystyle \text{Circumference}=24\pi\)

Example Question #272 : Radius

Find the circumference of the circle if the lengths of the legs of the inscribed isosceles triangle are \(\displaystyle 13\sqrt2\).

1

Possible Answers:

\(\displaystyle 90\)

\(\displaystyle 39\pi\)

\(\displaystyle 52\pi\)

\(\displaystyle 26\pi\)

Correct answer:

\(\displaystyle 26\pi\)

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.

\(\displaystyle \text{Hypotenuse}=13\sqrt2(\sqrt2)\)

Simplify.

\(\displaystyle \text{Hypotenuse}=26\)

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

\(\displaystyle \text{Hypotenuse}=\text{Diameter}=26\)

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.

\(\displaystyle \text{Circumference}=26\pi\)

Example Question #281 : Circles

Find the circumference of the circle if the lengths of the legs of the inscribed isosceles triangle are \(\displaystyle 13\).

1

Possible Answers:

\(\displaystyle 39\sqrt2\pi\)

\(\displaystyle 13\sqrt2\pi\)

\(\displaystyle 13\)

\(\displaystyle 26\sqrt2\pi\)

Correct answer:

\(\displaystyle 13\sqrt2\pi\)

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.

\(\displaystyle \text{Hypotenuse}=13\sqrt2\)

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

\(\displaystyle \text{Hypotenuse}=\text{Diameter}=13\sqrt2\)

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.

\(\displaystyle \text{Circumference}=13\sqrt2\pi\)

Learning Tools by Varsity Tutors