There is only one formula for the area of a circle:

Find the area of a circle with a diameter of 20 cm. Use the π button on your calculator, and give the answer correct to 1 dp.

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Plugging variables into an expression is essential for solving many algebra problems. See how to plug in variable values by watching this tutorial.

Trying to find the circumference of a circle? Know the diameter? Then you can use the formula for the circumference of a circle to get the answer! Just plug the value for the diameter into the formula and solve. This tutorial shows you how!

Check out this tutorial where you'll see exactly what order you need to follow when you simplify expressions. You'll also see what happens when you don't follow these rules, and you'll find out why order of operations is so important!

The diameter is 0.4m, so the Area will be:

Using the formulas above and additional formulas you can calculate properties of a given circle for any given variable.

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Furey, Edward "Circle Calculator" From http://www.CalculatorSoup.com - Online Calculator Resource.

You need to calculate π × 12 × 12 = 452.3893... and then round your answer to 3 s.f.

Want to find the radius of a circle? Already have the area? Then you can use the formula for the area of a circle to solve! This tutorial shows you how to use that formula and the given value for the area to find the radius. Take a look!

Use this calculator to find the area, circumference or radius of a circle.  Given any one variable of a circle you can calculate the other 2 unknowns.

You can't do algebra without working with variables, but variables can be confusing. If you've ever wondered what variables are, then this tutorial is for you!

This lesson is by Gisele Glosser. You can find me on Google.

Follow these steps to find the area of a circle. You will also learn how to find the area of a sector, which is a slice of a circle, similar in shape to a slice of pie or pizza.

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If you have the diameter of a circle, you can use it to find the area of that circle. Just plug that value into the formula for the area of a circle and solve. Watch this tutorial to see how it's done!

We must therefore remember to use the radius each time.

Find the area of a circle with a radius of 12 cm.

Estimate of Circle's Area = 80% of Square's Area = 80% of 9 = 7.2 m2

It is interesting to compare the area of a circle to a square:

The holes are circular (in cross section) because they are drilled out using an auger.

Did you know that you can figure out the formula for the area of a circle by first turning the circle into a parallelogram? It seems a little weird, but it really works! Watch this tutorial to see how it's done!

How to find the area of a circle

* Units: Note that units of length are shown for convenience.  They do not affect the calculations.  The units are in place to give an indication of the order of the results such as ft, ft2 or ft3.  Any other base unit can be substituted.

The holes are 0.4 m wide and 1 m deep, how much concrete should Max order for each hole?

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We have been told that the diameter is 20 cm. Therefore, the radius is 10 cm.

Use the π button on your calculator, and give your answer correct to 3 significant figures (s.f.).

Now to take a different angle on revision with this activity!

Circle's True Area = (π/4) × D2 = (π/4) × 32 = 7.07 m2 (to 2 decimals)

If you know the radius of a circle, you can use it to find the area of that circle. Just plug that value into the formula for the area of a circle and solve. Watch this tutorial to see how it's done!