Basic Geometry : How to find the length of the diameter

Study concepts, example questions & explanations for Basic Geometry

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Example Questions

Example Question #341 : Circles

Find the length of the diameter of a circle inscribed in a square that has a diagonal of \displaystyle 10.

Possible Answers:

\displaystyle 5\sqrt2

\displaystyle 5

\displaystyle 25\pi

\displaystyle 10\pi

Correct answer:

\displaystyle 5\sqrt2

Explanation:

13

When you draw out the circle that is inscribed in a square, you should notice two things. The first thing you should notice is that the diagonal of the square is also the hypotenuse of a right isosceles triangle that has the side lengths of the square as its legs. The second thing you should notice is that the diameter of the circle has the same length as the length of one side of the square.

First, use the Pythagorean theorem to find the length of a side of the square.

\displaystyle \text{Diagonal}^2=\text{side}^2+\text{side}^2

\displaystyle 2(\text{side})^2=\text{Diagonal}^2

\displaystyle \text{side}^2=\frac{\text{Diagonal}^2}{2}

\displaystyle \text{side}=\sqrt{\frac{\text{Diagonal}^2}{2}}=\frac{\text{Diagonal}\sqrt2}{2}

Substitute in the length of the diagonal to find the length of the square.

\displaystyle \text{side}=\frac{10(\sqrt2)}{2}

Simplify.

\displaystyle \text{side}=5\sqrt2

Now, recall the relationship between the diameter of the circle and the side of the square.

\displaystyle \text{diameter}=\text{side}=5\sqrt2

Example Question #342 : Plane Geometry

Find the length of the diameter of a circle inscribed in a square that has a diagonal of \displaystyle 20.

Possible Answers:

\displaystyle 5\sqrt2

\displaystyle 50

\displaystyle 200

\displaystyle 10\sqrt2

Correct answer:

\displaystyle 10\sqrt2

Explanation:

13

When you draw out the circle that is inscribed in a square, you should notice two things. The first thing you should notice is that the diagonal of the square is also the hypotenuse of a right isosceles triangle that has the side lengths of the square as its legs. The second thing you should notice is that the diameter of the circle has the same length as the length of one side of the square.

First, use the Pythagorean theorem to find the length of a side of the square.

\displaystyle \text{Diagonal}^2=\text{side}^2+\text{side}^2

\displaystyle 2(\text{side})^2=\text{Diagonal}^2

\displaystyle \text{side}^2=\frac{\text{Diagonal}^2}{2}

\displaystyle \text{side}=\sqrt{\frac{\text{Diagonal}^2}{2}}=\frac{\text{Diagonal}\sqrt2}{2}

Substitute in the length of the diagonal to find the length of the square.

\displaystyle \text{side}=\frac{20(\sqrt2)}{2}

Simplify.

\displaystyle \text{side}=10\sqrt2

Now, recall the relationship between the diameter of the circle and the side of the square.

\displaystyle \text{diameter}=\text{side}=10\sqrt2

Example Question #41 : How To Find The Length Of The Diameter

Find the length of the diameter of a circle inscribed in a square that has a diagonal of \displaystyle 24.

Possible Answers:

\displaystyle 6\sqrt2

\displaystyle 18\pi

\displaystyle 12\sqrt2

\displaystyle 24\pi

Correct answer:

\displaystyle 12\sqrt2

Explanation:

13

When you draw out the circle that is inscribed in a square, you should notice two things. The first thing you should notice is that the diagonal of the square is also the hypotenuse of a right isosceles triangle that has the side lengths of the square as its legs. The second thing you should notice is that the diameter of the circle has the same length as the length of one side of the square.

First, use the Pythagorean theorem to find the length of a side of the square.

\displaystyle \text{Diagonal}^2=\text{side}^2+\text{side}^2

\displaystyle 2(\text{side})^2=\text{Diagonal}^2

\displaystyle \text{side}^2=\frac{\text{Diagonal}^2}{2}

\displaystyle \text{side}=\sqrt{\frac{\text{Diagonal}^2}{2}}=\frac{\text{Diagonal}\sqrt2}{2}

Substitute in the length of the diagonal to find the length of the square.

\displaystyle \text{side}=\frac{24(\sqrt2)}{2}

Simplify.

\displaystyle \text{side}=12\sqrt2

Now, recall the relationship between the diameter of the circle and the side of the square.

\displaystyle \text{diameter}=\text{side}=12\sqrt2

Example Question #344 : Circles

Find the length of the diameter of a circle inscribed in a square that has a diagonal of \displaystyle 26.

Possible Answers:

\displaystyle 26\pi

\displaystyle 14\sqrt2

\displaystyle 13\sqrt2

\displaystyle \frac{13}{2}\sqrt2

Correct answer:

\displaystyle 13\sqrt2

Explanation:

13

When you draw out the circle that is inscribed in a square, you should notice two things. The first thing you should notice is that the diagonal of the square is also the hypotenuse of a right isosceles triangle that has the side lengths of the square as its legs. The second thing you should notice is that the diameter of the circle has the same length as the length of one side of the square.

First, use the Pythagorean theorem to find the length of a side of the square.

\displaystyle \text{Diagonal}^2=\text{side}^2+\text{side}^2

\displaystyle 2(\text{side})^2=\text{Diagonal}^2

\displaystyle \text{side}^2=\frac{\text{Diagonal}^2}{2}

\displaystyle \text{side}=\sqrt{\frac{\text{Diagonal}^2}{2}}=\frac{\text{Diagonal}\sqrt2}{2}

Substitute in the length of the diagonal to find the length of the square.

\displaystyle \text{side}=\frac{26(\sqrt2)}{2}

Simplify.

\displaystyle \text{side}=13\sqrt2

Now, recall the relationship between the diameter of the circle and the side of the square.

\displaystyle \text{diameter}=\text{side}=13\sqrt2

Example Question #41 : Diameter

Find the length of the diameter of a circle inscribed in a square that has a diagonal of \displaystyle 36.

Possible Answers:

\displaystyle 18\sqrt2

\displaystyle 54\sqrt2

\displaystyle 18

\displaystyle 72

Correct answer:

\displaystyle 18\sqrt2

Explanation:

13

When you draw out the circle that is inscribed in a square, you should notice two things. The first thing you should notice is that the diagonal of the square is also the hypotenuse of a right isosceles triangle that has the side lengths of the square as its legs. The second thing you should notice is that the diameter of the circle has the same length as the length of one side of the square.

First, use the Pythagorean theorem to find the length of a side of the square.

\displaystyle \text{Diagonal}^2=\text{side}^2+\text{side}^2

\displaystyle 2(\text{side})^2=\text{Diagonal}^2

\displaystyle \text{side}^2=\frac{\text{Diagonal}^2}{2}

\displaystyle \text{side}=\sqrt{\frac{\text{Diagonal}^2}{2}}=\frac{\text{Diagonal}\sqrt2}{2}

Substitute in the length of the diagonal to find the length of the square.

\displaystyle \text{side}=\frac{36(\sqrt2)}{2}

Simplify.

\displaystyle \text{side}=18\sqrt2

Now, recall the relationship between the diameter of the circle and the side of the square.

\displaystyle \text{diameter}=\text{side}=18\sqrt2 

Example Question #351 : Circles

Find the length of the diameter of a circle inscribed in a square that has a diagonal of \displaystyle 48.

Possible Answers:

\displaystyle 24\sqrt2

\displaystyle 12\sqrt2

\displaystyle 48\sqrt2

\displaystyle 6\sqrt2

Correct answer:

\displaystyle 24\sqrt2

Explanation:

13

When you draw out the circle that is inscribed in a square, you should notice two things. The first thing you should notice is that the diagonal of the square is also the hypotenuse of a right isosceles triangle that has the side lengths of the square as its legs. The second thing you should notice is that the diameter of the circle has the same length as the length of one side of the square.

First, use the Pythagorean theorem to find the length of a side of the square.

\displaystyle \text{Diagonal}^2=\text{side}^2+\text{side}^2

\displaystyle 2(\text{side})^2=\text{Diagonal}^2

\displaystyle \text{side}^2=\frac{\text{Diagonal}^2}{2}

\displaystyle \text{side}=\sqrt{\frac{\text{Diagonal}^2}{2}}=\frac{\text{Diagonal}\sqrt2}{2}

Substitute in the length of the diagonal to find the length of the square.

\displaystyle \text{side}=\frac{48(\sqrt2)}{2}

Simplify.

\displaystyle \text{side}=24\sqrt2

Now, recall the relationship between the diameter of the circle and the side of the square.

\displaystyle \text{diameter}=\text{side}=24\sqrt2

Example Question #42 : Diameter

Find the length of the diameter given the area is \displaystyle 16\pi.

Possible Answers:

\displaystyle 8

\displaystyle 4

\displaystyle 12

\displaystyle 16

Correct answer:

\displaystyle 8

Explanation:

To solve, simply use the formula for area to solve for the radius and multiply by 2.

\displaystyle A=\pi{r^2}\Rightarrow r=\sqrt{\frac{A}{\pi}}

\displaystyle r=\sqrt{\frac{16\pi}{\pi}}=\sqrt{16}=4

\displaystyle d=2r=2*4=8

Example Question #353 : Circles

The circumference of a circle is equal to \displaystyle 251.33 units. Find the length of the diameter of this circle. 

Possible Answers:

\displaystyle 60 units

\displaystyle 70 units

\displaystyle 40 units

\displaystyle 90 units

\displaystyle 80 units

Correct answer:

\displaystyle 80 units

Explanation:

There are two steps to finding the answer to this question. The first is to find the radius through the formula for the circumference of a circle.

\displaystyle Area = 2 (\pi) (r)

Then we plug in numbers and solve. 

\displaystyle 251.33 = 2 (\pi) (r)

\displaystyle 125.7 = \pi (r)

\displaystyle 40 = radius

Now that we have found the radius, we solve for diameter by doubling it, since..

\displaystyle Diameter = 2(Radius)

Therefore, the diameter is equal to \displaystyle 80 units

Example Question #43 : Diameter

Find the length of the diameter given radius is 7.

Possible Answers:

\displaystyle 49\pi

\displaystyle 28\pi

\displaystyle 14

\displaystyle 14\pi

Correct answer:

\displaystyle 14

Explanation:

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

Recall that the diameter of a circle is twice the radius of the circle.

Given that the radius is seven, multiply it by 2 to solve for the diameter.

Thus,

\displaystyle \\d=2r\\d=2*7\\d=14.

Example Question #44 : Diameter

Find the length of the diameter of a circle given an area of  \displaystyle 9\pi.

Possible Answers:

\displaystyle 9

\displaystyle 6\pi

\displaystyle 3

\displaystyle 6

Correct answer:

\displaystyle 6

Explanation:

To solve, simply use the formula for the area to find the length of the radius and then multiply that by 2 to find the diameter. Thus,

\displaystyle A=\pi{r^2}\Rightarrow r=\sqrt{\frac{A}{\pi}}

\displaystyle r=\sqrt{\frac{9\pi}{\pi}}=\sqrt9=3

\displaystyle d=2r=2*3=6

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