Let the number of sides be x and by solving the equation for diagonals 0.5(x*x-3x) = 135 the solution is -15 or 18 and so therefore it has 18 sides irrespective if it is an irregular or a regular polygon
how many diagonals are there iin a polygon of 11 sides
That polygon is called a "triangle". It has no diagonals.
A 7 sided polygon has 14 diagonals
There are 77 diagonals
38 diagonals
An heptagon has 7 sides and 14 diagonals
It will have ten sides
A polygon with 14 diagonals will have 7 sides
9
18
7
7