Finding the radius of a circle

Step by step directions for finding the radius of a circle. If you are given the area how do you find the radius of the circle?
I like to call this a backwards problem because most people understand how to calculate the area of a circle, and this skill can be used to find the radius.

You are given the area of a square ,and we have to find the radius? We don't know the radius of this circle which is all this space inside the circle
The area is 81pi inches squared
Step 1. Write down the area formula
The area of a square is pi radius squared. What I will do is take the formula and set it equal to what we know.
Pi radius squared is equal to 81 pi
Notice we have a pi on both sides. If I divide both sides by pi which is just the constant 3.14 you can get rid of pi and you are just left with radius squared equals 81
Next take the square root of both sides, so the radius is equal to 9.When you take the square root you typically take a positive and negative root ,but because this is a length we know the length of a radius can't be negative therefore it must be a positive answer
The radius of a circle is equal to positive 9 and the unit measure is inches so we will go back and add inches to our solution
There you go ,that’s how you find the radius of a circle given the area

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For more on circles,area, and radius see

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[brianmoore]

Really helpful video helped me a lot with my homework thank you so much

[samdekoning]

Thank u first video I clicked was this you explained it perfectly

[maggiereeve]

xD you were fast talking But I am too So all I did was Right Fast and Got it. Thx so much

[palestlatina]

What if I dont have the are I only have the diameter