# #19. Given a regular octagon, find the measures of the angles formed by (a) two consecutive radii and (b) a radius and a side of the polygon.

## A regular octagon forms 8 congruent isosceles triangles, where the central angles are 360/8° or 45° each.

Your second part cannot be answered since you gave no data.

Let the radius be r and consider one of the triangles..

If the base is 2s, then

s/r = sin 67.5°

s = r sin 67.5°

and 2s = 2r sin 67.5°

So for any given radius, you can find the side, and for any given side, you can find the radius using the above relationship

## thx @Reiny

## To find the measures of the angles formed by two consecutive radii in a regular octagon, we can use the formula:

angle = 360 degrees / number of sides

Since the octagon has 8 sides, the angle formed by two consecutive radii is:

angle = 360 degrees / 8

= 45 degrees

So, the measure of the angle formed by two consecutive radii in a regular octagon is 45 degrees.

To find the measure of the angle formed by a radius and a side of the polygon, we need to find the measure of the central angle of the octagon.

The formula to find the measure of the central angle in a regular polygon is:

central angle = 360 degrees / number of sides

In this case, the central angle of the octagon is:

central angle = 360 degrees / 8

= 45 degrees

Since the central angle and the angle formed by a radius and a side of the polygon are supplementary angles (they add up to 180 degrees), the measure of the angle formed by a radius and a side of the octagon is:

angle = 180 degrees - central angle

= 180 degrees - 45 degrees

= 135 degrees

So, the measure of the angle formed by a radius and a side of a regular octagon is 135 degrees.

## To find the measures of the angles formed by two consecutive radii and a radius and a side of a regular octagon, we can use the properties of regular polygons.

(a) Two consecutive radii:

In a regular octagon, all angles are equal. The sum of the interior angles of an octagon is given by the formula (n-2) * 180 degrees, where n is the number of sides. For an octagon, this is (8-2) * 180 = 1080 degrees.

Since all angles are equal in a regular octagon, each angle measures 1080 degrees / 8 = 135 degrees.

Therefore, the measure of each angle formed by two consecutive radii in a regular octagon is 135 degrees.

(b) A radius and a side:

To find the measure of the angle formed by a radius and a side, we need to find the central angle of the octagon. The central angle can be calculated by dividing 360 degrees (the total angle measure of a circle) by the number of sides of the polygon.

For an octagon, the central angle is 360 degrees / 8 = 45 degrees.

The measure of the angle formed by a radius and a side is half of the central angle. Therefore, the measure of each angle formed by a radius and a side in a regular octagon is 45 degrees / 2 = 22.5 degrees.

Therefore, the measures of the angles formed by two consecutive radii and a radius and a side of a regular octagon are 135 degrees and 22.5 degrees, respectively.