Question

Learning Task 2

Solve the following problems. (Show your complete solutions.)
1.) What is the sum of the interior angles of a polygon having 8 sides?
2.) Find the measure of the exterior angle of a regular decagon.
3.) Find the number of diagonals of a nonagon.
4.) What is the measure of each angle of a regular nonagon?
5.) if the sum of the measures of the angles of a regular polygon is 900, then
what is the number of sides?

Answer 1

1. 1080°

2. 36°

3. 27 diagonals

4. 140°

5. 7 sides

Explanation:

1. The sum S of the interior angles of a polygon is given by;

S = (n-2) x 180°

Where;

n = number of sides of the polygon.

Therefore, to get the sum of the interior angles of a polygon having 8 sides, we substitute n = 8 into equation (i) as follows;

S = (8 - 2) x 180°

S = 6 x 180°

S = 1080°

Therefore, the sum of the interior angles of a polygon having 8 sides is 1080°

2. The sum of interior angles of a polygon is given by;

S = (n - 2) x 180°

For a polygon which is a regular decagon where the number of sides n = 10, the sum is;

S = (10 - 2) x 180°

S = 8 x 180°

S = 1440°

Since the decagon is regular, then each of its interior angles is given by;

1440° / 10

=> 144°

Now, since we know that the sum of the interior angle and exterior angle will give 180°, then;

The exterior angle of a regular decagon is;

180° - 144° = 36°

Therefore, the exterior angle of a regular decagon is 36°

3. The number of diagonals N of a polygon with n sides is given by;

N =
`(1)/(2) n(n-3)`

So, for a nonagon which has 9 sides (i.e n = 9), the number of diagonals is;

N =
`(1)/(2)*9(9-3)`

N =
`(1)/(2)*9(6)`

N = 9(3)

N = 27

Therefore, a nonagon has 27 diagonals.

4. The sum of interior angles of a polygon is given by;

S = (n - 2) x 180°

For a polygon which is a nonagon where the number of sides n = 9, the sum is;

S = (9 - 2) x 180°

S = 7 x 180°

S = 1260°

Since the nonagon is regular, then each of its interior angles is given by;

1260° / 9

=> 140°

Therefore, the measure of each angle (interior angle) of a regular nonagon is 140°

5. The sum of the interior angles of a polygon is given by;

S = (n - 2) x 180°

So if the sum is 900, then to get the number of sides of the polygon, we substitute S = 900 into the equation;

900° = (n - 2) x 180°

Divide through by 180°

5 = (n - 2)

Solve for n;

n = 5 + 2

n = 7

Therefore, the regular polygon has 7 sides.