# Basic Geometry : How to find the area of a circle

## Example Questions

### Example Question #101 : Radius

Find the area of a circle that is inscribed in a square that has a diagonal of .

Explanation:

When you draw out the circle that is inscribed in a square, you should notice two things. The first thing you should notice is that the diagonal of the square is also the hypotenuse of a right isosceles triangle that has the side lengths of the square as its legs. The second thing you should notice is that the diameter of the circle has the same length as the length of one side of the square.

First, use the Pythagorean theorem to find the length of a side of the square.

Substitute in the length of the diagonal to find the length of the square.

Simplify.

Now, recall the relationship between the diameter of the circle and the side of the square.

Now, recall that the radius is half the length of the diameter.

Substitute in the value o fthe diameter to find the length of the radius.

Solve.

Now, recall the formula to find the area of a circle.

Substitute in the value of the radius to find the area of the circle.

Solve.

### Example Question #102 : How To Find The Area Of A Circle

Find the area of a circle that is inscribed in a square that has a diagonal of .

Explanation:

When you draw out the circle that is inscribed in a square, you should notice two things. The first thing you should notice is that the diagonal of the square is also the hypotenuse of a right isosceles triangle that has the side lengths of the square as its legs. The second thing you should notice is that the diameter of the circle has the same length as the length of one side of the square.

First, use the Pythagorean theorem to find the length of a side of the square.

Substitute in the length of the diagonal to find the length of the square.

Simplify.

Now, recall the relationship between the diameter of the circle and the side of the square.

Now, recall that the radius is half the length of the diameter.

Substitute in the value o fthe diameter to find the length of the radius.

Solve.

Now, recall the formula to find the area of a circle.

Substitute in the value of the radius to find the area of the circle.

Solve.

### Example Question #103 : How To Find The Area Of A Circle

Find the area of a circle that is inscribed in a square that has a diagonal of .

Explanation:

When you draw out the circle that is inscribed in a square, you should notice two things. The first thing you should notice is that the diagonal of the square is also the hypotenuse of a right isosceles triangle that has the side lengths of the square as its legs. The second thing you should notice is that the diameter of the circle has the same length as the length of one side of the square.

First, use the Pythagorean theorem to find the length of a side of the square.

Substitute in the length of the diagonal to find the length of the square.

Simplify.

Now, recall the relationship between the diameter of the circle and the side of the square.

Now, recall that the radius is half the length of the diameter.

Substitute in the value o fthe diameter to find the length of the radius.

Solve.

Now, recall the formula to find the area of a circle.

Substitute in the value of the radius to find the area of the circle.

Solve.

### Example Question #101 : How To Find The Area Of A Circle

Find the area of a circle given radius 4.

Explanation:

To solve, simply use the formula for the area of a circle. Thus,

### Example Question #102 : How To Find The Area Of A Circle

If a rectangle with a diagonal of  is inscribed in a circle, what is the area of the circle?

Cannot be determined.

Explanation:

Notice that the diagonal of the rectangle is the same as the diameter of the circle.

Now, recall the relationship between the diameter of a circle and its radius:

Substitute in the given diameter to find the radius of the circle.

Simplify.

Finally, recall how to find the area of a circle:

Substitute in the value of the radius to find the area.

Solve.

### Example Question #103 : How To Find The Area Of A Circle

If a rectangle with a diagonal of  is inscribed in a circle, what is the area of the circle?

Explanation:

Notice that the diagonal of the rectangle is the same as the diameter of the circle.

Now, recall the relationship between the diameter of a circle and its radius:

Substitute in the given diameter to find the radius of the circle.

Simplify.

Finally, recall how to find the area of a circle:

Substitute in the value of the radius to find the area.

Solve.

### Example Question #104 : How To Find The Area Of A Circle

If a rectangle with a diagonal of  is inscribed in a circle, what is the area of the circle?

Explanation:

Notice that the diagonal of the rectangle is the same as the diameter of the circle.

Now, recall the relationship between the diameter of a circle and its radius:

Substitute in the given diameter to find the radius of the circle.

Simplify.

Finally, recall how to find the area of a circle:

Substitute in the value of the radius to find the area.

Solve.

### Example Question #105 : How To Find The Area Of A Circle

If a rectangle with a diagonal of  is inscribed in a circle, what is the area of the circle?

Explanation:

Notice that the diagonal of the rectangle is the same as the diameter of the circle.

Now, recall the relationship between the diameter of a circle and its radius:

Substitute in the given diameter to find the radius of the circle.

Simplify.

Finally, recall how to find the area of a circle:

Substitute in the value of the radius to find the area.

Solve.

### Example Question #106 : How To Find The Area Of A Circle

If a rectangle with a diagonal of  is inscribed in a circle, what is the area of the circle?

Explanation:

Notice that the diagonal of the rectangle is the same as the diameter of the circle.

Now, recall the relationship between the diameter of a circle and its radius:

Substitute in the given diameter to find the radius of the circle.

Simplify.

Finally, recall how to find the area of a circle:

Substitute in the value of the radius to find the area.

Solve.

### Example Question #107 : How To Find The Area Of A Circle

If a rectangle with a diagonal of  is inscribed in a circle, what is the area of the circle?

Explanation:

Notice that the diagonal of the rectangle is the same as the diameter of the circle.

Now, recall the relationship between the diameter of a circle and its radius:

Substitute in the given diameter to find the radius of the circle.

Simplify.

Finally, recall how to find the area of a circle:

Substitute in the value of the radius to find the area.

Solve.