# How do you find the radius from 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.

A.

### 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.#### How do you get the circumference of a circle with the radius?

The**circumference**= π x the diameter of the circle (Pi multiplied by the diameter of the circle). Simply divide the**circumference**by π and you will have the length of the diameter. The diameter is just the**radius**times two, so divide the diameter by two and you will have the**radius**of the circle!#### 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.#### 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.

B.

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

To work out the area of a

**semicircle**you can use the formula A = (Pi*r^2)/2. This is because the area of a full circle is A = Pi*r^2 and a**semicircle**is half the area of a full circle so you divide this by 2. Just be careful to substitute the**radius**into the formula and not the diameter!#### How do you find the area of a quadrant?

Substitute r = 8 directly into the formula A = ¼ πr². As you can see it gives exactly the same answer as method 1. Work out the**area**of this**quadrant**(radius 3.8m). = 14.44π (leave the answer as an exact solution as this need to be divided by 4).#### What is a minor arc of a circle?

A**minor arc**(left figure) is an**arc of a circle**having measure less than or equal to ( radians). SEE ALSO:**Arc**,**Major Arc**, Semicircle. REFERENCES: Rhoad, R.; Milauskas, G.; and Whipple, R. Geometry for Enjoyment and Challenge, rev. ed.#### How do you calculate the square root of a number?

**To start finding a square root via prime factorization, first, try to reduce your number into its perfect square factors.**- Let's use an example. We want to find the square root of 400 by hand. To begin, we would divide the number into perfect square factors.
- We would write this as: Sqrt(400) = Sqrt(25 × 16)

C.

### How do you find diameter from 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.#### How do you work out a circumference of a circle?

Plug in the numbers to solve for C. Now we know that 2πr = C. Look back at the original math problem to see what r (the radius) equals. Then replace π with 3.14, or use a calculator's π button to get a more accurate answer. Multiply 2πr together using these numbers. The answer you get is the**circumference**.#### How do you figure out the perimeter of a circle?

We know the formula to**find**the**perimeter**of the**circle**if the diameter is given, namely π D. Substitute the diameter 4.4 and Pi value as 3.14 in the above formula. Therefore 13.82 cm is the**perimeter**of the given**circle**.#### How do you find the area with the circumference?

The**area**of a circle is given by the formula A = π r^{2}, where A is the**area**and r is the radius. The**circumference**of a circle is C = 2 π r. If we "solve for r" in the second equation, we have r = C / (2 π ).

Updated: 20th September 2018