interior angle of a regular 18-gon.
It is easier to calculate the exterior angle of a regular polygon of n-sides (n-gon) by the relation
exterior angle = 360/n
For a 18-gon, n=18, so exterior angle = 360/18=20 °
The value of each interior angle is therefore the supplement, or
Interior angle = 180-20=160 degrees.
Naming of a 9-gon
A polygon with 9 vertices is called a nonagon (in English) or enneagon (French ennéagone, but the English version is sometimes used)
You had a good start with the correct answer.
Exterior angle of a 15-gon
The exterior angle of a 15-gon can be calculated using the relation given in the first paragraph, namely
Exterior angle = 360/15=24 degrees
The chapter 7 test will have 20-30 questions on it. Novanet!
Answer:
the answer is -3
its just opposite to the normal when we check negative numbers.
Given:
Sides of triangles in the options.
To find:
Which could NOT be the lengths of the sides of a triangle.
Solution:
Condition for triangle:
Sum of two smaller sides of a triangle must be greater than the longest side.
In option A,

Sides 5 in, 5 in, 5 in are the lengths of the sides of a triangle.
In option B,

Sides 10 cm, 15 cm, 20 cm are the lengths of the sides of a triangle.
In option C,

Sides 3 in, 4 in, 5 in are the lengths of the sides of a triangle.
In option D,

Since, the sum of two smaller sides is less than the longest side, therefore the sides 8 ft, 15 ft, 5 ft are not the lengths of the sides of a triangle.
Therefore, the correct option is D.