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Find x in the following figures.
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(a) |
(b) |
Sum of internal and external angle at a vertex=180°.
sum of external angles of a polygon=360°
using these 2 properties, we can find out the value of x.
(a)sum of external angles=125+125+x=360
250+x=360
x=360-250=110°
(b)sum of external angles=60+90+70+x+90=360
310+x=360
x=360-310=50°
Find the measure of each exterior angle of a regular polygon of
(i) 9 sides
(ii) 15 sides
(i) Sum of all exterior angles of the given polygon = 360º
Each exterior angle of a regular polygon has the same measure.
Thus, measure of each exterior angle of a regular polygon of 9 sides
= 
(ii) Sum of all exterior angles of the given polygon = 360º
Each exterior angle of a regular polygon has the same measure.
Thus, measure of each exterior angle of a regular polygon of 15 sides
= 
How many sides does a regular polygon have if the measure of an exterior angle is 24°?
since it is a regular polygon all exterior angles are equal.
sum of exterior angles of a regular polygon=360°
number of sides =sum of angles/angle measure=360/24=15
How many sides does a regular polygon have if each of its interior angles is 165°?
Measure of each interior angle = 165°
Measure of each exterior angle = 180° − 165° = 15°
The sum of all exterior angles of any polygon is 360º.
Thus, number of sides of the polygon
(a) Is it possible to have a regular polygon with measure of each exterior angle as 22°?
(b) Can it be an interior angle of a regular polygon? Why?
The sum of all exterior angles of all polygons is 360º. Also, in a regular polygon, each exterior angle is of the same measure. Hence, if 360º is a perfect multiple of the given exterior angle, then the given polygon will be possible.
(a) Exterior angle = 22°
360º is not a perfect multiple of 22º. Hence, such polygon is not possible.
(b) Interior angle = 22°
Exterior angle = 180° − 22° = 158°
Such a polygon is not possible as 360° is not a perfect multiple of 158°.
(a) What is the minimum interior angle possible for a regular polygon?
(b) What is the maximum exterior angle possible for a regular polygon?
Consider a regular polygon having the lowest possible number of sides (i.e., an equilateral triangle). The exterior angle of this triangle will be the maximum exterior angle possible for any regular polygon.
Exterior angle of an equilateral triangle 
Hence, maximum possible measure of exterior angle for any polygon is 120º. Also, we know that an exterior angle and an interior angle are always in a linear pair.
Hence, minimum interior angle = 180º − 120° = 60º
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