# High School Math : Geometry

## Example Questions

### Example Question #1 : How To Find The Angle Of A Sector

The length of an arc, , of a circle is  and the radius, , of the circle is . What is the measure in degrees of the central angle, , formed by the arc ?

Explanation:

The circumference of the circle is .

The length of the arc S is .

A ratio can be established:

Solving for yields 90o

Note: This makes sense. Since the arc S was one-fourth the circumference of the circle, the central angle formed by arc S should be one-fourth the total degrees of a circle.

### Example Question #1 : How To Find The Angle Of A Sector

In the circle above, the length of arc BC is 100 degrees, and the segment AC is a diameter. What is the measure of angle ADB in degrees?

80

40

90

cannot be determined

100

40

Explanation:

Since we know that segment AC is a diameter, this means that the length of the arc ABC must be 180 degrees. This means that the length of the arc AB must be 80 degrees.

Since angle ADB is an inscribed angle, its measure is equal to half of the measure of the angle of the arc that it intercepts. This means that the measure of the angle is half of 80 degrees, or 40 degrees.

### Example Question #2 : How To Find The Angle Of A Sector

What is the angle of a sector of area   on a circle having a radius of ?

Explanation:

To begin, you should compute the complete area of the circle:

For your data, this is:

Now, to find the angle measure of a sector, you find what portion of the circle the sector is. Here, it is:

Now, multiply this by the total  degrees in a circle:

Rounded, this is .

### Example Question #3 : How To Find The Angle Of A Sector

What is the angle of a sector that has an arc length of   on a circle of diameter  ?

Explanation:

The first thing to do for this problem is to compute the total circumference of the circle. Notice that you were given the diameter. The proper equation is therefore:

For your data, this means,

Now, to compute the angle, note that you have a percentage of the total circumference, based upon your arc length:

Rounded to the nearest hundredth, this is .

### Example Question #1 : How To Find The Area Of A Circle

What is the area of a circle with a radius of ?

Explanation:

To find the area of a circle you must plug the radius into  in the following equation.

In this case, the radius is , so we plug  into .

### Example Question #2 : How To Find The Area Of A Circle

What is the area of a circle with a radius of 9?

Explanation:

To find the area of a circle you must plug the radius into  in the following equation

In this case the radius is 9 so we plug it into  to get

We then multiply it by  to get our answer

### Example Question #3 : How To Find The Area Of A Circle

Find the area of a circle with a radius of .

Not enough information to solve

Explanation:

In order to find the circle's area, utilize the formula .

### Example Question #4 : How To Find The Area Of A Circle

A circle has a radius , what is its area?

Not enough information to solve

Explanation:

In order to find the circle's area, utilize the formula .

### Example Question #5 : How To Find The Area Of A Circle

A circle has a diameter , what is its area?

Not enough information to solve

Explanation:

In order to find the circle's area, utilize the formula .

However, we need to convert our diameter into a radius.

Solve for .

Insert the radius into the area formula and solve.

### Example Question #6 : How To Find The Area Of A Circle

Refer to the above drawing. This shows a ring-shaped garden with inner radius 20 feet and outer radius 40 feet. To the nearest square foot, what is the area of the garden?