Just remember to divide the diameter by two to get the

**radius**. If you were asked to**find**the**radius**instead of the diameter, you would simply divide 7 feet by 2 because the**radius**is one-half the**measure**of the diameter. The**radius**of the circle is 3.5 feet. You can also use the circumference and**radius equation**.1

## What is the equation of a circle?

The center-radius form of the circle equation is in the format (x – h)

^{2}+ (y – k)^{2}= r^{2}, with the center being at the**point**(h, k) and the radius being "r". This form of the equation is helpful, since you can easily find the center and the radius.2

## What is a chord of a circle?

A

**chord of a circle**is a straight line segment whose endpoints both lie on the**circle**. A secant line, or just secant, is the infinite line extension of a**chord**. More generally, a**chord**is a line segment joining two points on any curve, for instance an ellipse. The word**chord**is from the Latin chorda meaning bowstring.3

## What is the radius of the circle?

The circumference is the outside perimeter of a

**circle**. It's the distance around a**circle**. A**radius**can be a line from any point on the circumference to the center of the**circle**. If you put two**radii**together, edge to edge, going through the center of a**circle**, you would get a diameter.4

## What is pi the ratio of?

**Pi**(π), the 16th letter of the Greek alphabet, is used to represent the most widely known mathematical constant. By definition,

**pi**is the

**ratio of**the circumference of a circle to its diameter. Conversely, the circumference is equal to

**pi**times the diameter (c = πd).

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## How do you find the radius of a circle when you know the area?

**Method 2**

**Using the Area**

- Set up the formula for the area of a circle. The formula is A = π r 2 {displaystyle A=pi r^{2}} , where A {displaystyle A} equals the area of the circle, and r {displaystyle r} equals the radius.
- Solve for the radius.
- Plug the area into the formula.
- Divide the area by .
- Take the square root.

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## How do I find the diameter of a circle if I know the area?

**For an example, we have an area of 303,000 square meters.**

- Divide the area (in square units) by Pi (approximately 3.14159). Example: 303,000/3.14159 = 96447.98.
- Take the square root of the result (Example: 310.56). This is the radius.
- Now double the radius to get the diameter (Example: 621.12 meters).

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## What is the formula for the diameter?

The diameter is the measurement across the circle passing through the center. The two formulas involving the diameter are the one that says the diameter is twice the

**radius**and the one that says the**circumference**is the diameter times pi.8

## How do you find the circumference of a circle with only the area?

**Steps**

- Use the formula for the area of a circle, π*r^2, or pi times radius r squared = Area A.
- Use the formula for the circumference of a circle, 2*π*r, or 2 times pi time radius r = Circumference C.
- Isolate r in the formula for the area, so divide by π, then take the square root: sqrt(A/π)

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## What is the diameter if you know the circumference?

Solve the equation for the

**diameter**of the circle, d= C/π. In this example, "d = 12 / 3.14." or "The**diameter**is equal to twelve divided by 3.14." Divide the**circumference**by pi to get the answer. In this case, the**diameter**would be 3.82 inches.10

## What is diameter and radius?

**Radius**,

**Diameter**and Circumference. The

**Radius**is the distance from the center outwards. The

**Diameter**goes straight across the circle, through the center. The Circumference is the distance once around the circle.

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## What is the formula to the circumference of a circle?

Keeping this in mind, you can write down the

**formula**for finding the**circumference**of a circle given the radius: C = 2πr. In this**formula**, "r" represents the radius of the circle. Again, you can plug π into your calculator to get its numeral value, which is a closer approximation of 3.14.12

## How do you find out the radius of a cylinder?

First, divide the diameter by 2 and plug the values for volume, pi, and

**radius**into the formula for volume of a**cylinder**. Next, square the**radius**and multiply the values together. Then, divide both sides by 200.96 for the answer, remembering to include the appropriate unit of measurement.13

## How do you calculate the area of a circle?

To find the

**area**of a**circle**with the radius, square the radius, or multiply it by itself. Then, multiply the squared radius by pi, or 3.14, to get the**area**. To find the**area**with the diameter, simply divide the diameter by 2, plug it into the radius formula, and solve as before.14

## How can you find the circumference of a circle?

**How to find the circumference of a circle:**

- The circumference of a circle can be found by multiplying pi ( π = 3.14 ) by the diameter of the circle.
- If a circle has a diameter of 4, its circumference is 3.14*4=12.56.
- If you know the radius, the diameter is twice as large.

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## Where is the circumference of a circle?

The distance around a

**circle**on the other hand is called the**circumference**(c). Half of the diameter, or the distance from the midpoint to the**circle**border, is called the radius of the**circle**(r).16

## How do you find the radius of a sphere?

**Method 1**

**Using Radius Calculation Formulas**

- Find the radius if you know the diameter. The radius is half the diameter, so use the formula r = D/2.
- Find the radius if you know the circumference. Use the formula C/2π.
- Calculate the radius if you know the volume of a sphere.
- Find the radius from the surface area.

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## What is the unit for the area of a circle?

Because the radius of a circle is equal to half its diameter, these equations are essentially the same. The units for area can be any unit for the measure of length squared: feet squared (ft

^{2}), meters squared (m^{2}), centimeters squared (cm^{2}),**etc**.18

## What is the formula for the circumference of a?

**Circumference Formula**. The

**circumference formula**is used to calculate the distance around a circle.

**Circumference formulas**: C = 2πr or C = πd. r is the radius and d is the diameter.

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## How do you find the diameter of a circle?

The radius is the distance from the center of the circle to its edge. For example, if the radius of the circle is 4 cm, then the

**diameter**of the circle is 4 cm x 2, or 8 cm. If you know the circumference of the circle, divide it by π to get the**diameter**.