Area of a Circle

Area of a Circle - How it Works - Video

Example 1

Example 1:

To find the area of a circle, we need to use the formula, and that is Area =πr2, where r is the radius. The image gives us the radius as 7 cm.

So our first step is to substitute the 7 cm into the formula, Area = π*(7)2 .

Next we have to square, 7, ==> 49 because 7*7 = 49. So we now have Area = π*49.

Next we have flip the number and π. So our final answer is Area = 49π cm2 .

Now sometimes, we are asked to have our as decimal, and in that case we multiply 49 and π, and we get 153.94 cm2 .

Example 2

Example 2:

To find the area of a circle, we need to use the formula, and that is Area =πr2, where r is the radius. The image gives us the diameter as 12 cm.

So our first step is divide the diameter by 2 since the diameter is double the radius ==> 12 cm / 2 = 6 cm.

So our next step is to substitute the 6 cm into the formula, Area = π*(6)2 .

Next we have to square, 6, ==> 49 because 6*6 = 36. So we now have Area = π*36.

Next we have flip the number and π. So our final answer is Area = 36π cm2 .

Now sometimes, we are asked to have our as decimal, and in that case we multiply 36 and π, and we get 113.10 cm2 .

Example 3

Example 3:

To find the area of a circle, we need to use the formula, and that is Area =πr2, where r is the radius. The image gives us the area as 49π m2.

So our first step is set up the equation ==> 49π = π*r2.

Our next step is to do an inverse step and divide each side by π.

Now we have 49 = r2. We must have r and not *r2. So the next step is to take the square root of each because that is the inverse of square. After taking the square root of each side we have r = 7 or -7. Since we can't have a negative side length, we can cancel the -7.

So our final answer is the radius is 7 m.

Example 4

Example 4:

To find the area of a circle, we need to use the formula, and that is Area =πr2, where r is the radius. The image gives us the area as 64π m2.

So our first step is set up the equation ==> 64π = π*r2.

Our next step is to do an inverse step and divide each side by π.

Now we have 64 = r2. We must have r and not *r2. So the next step is to take the square root of each because that is the inverse of square. After taking the square root of each side we have r = 8 or -8. Since we can't have a negative side length, we can cancel the -8. So our radius is 8 cm.

To find the diameter, we multiply the radius by 2 ==> 8*2 = 16 cm. So our answer is the diameter is 16 cm.

Live Worksheet

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