Answer:
540°
Step-by-step explanation:
The number of diagonals in a polygon with n sides is ...
d = n(n -3)/2
If this value is equal to the number of sides, n, then we must have ...
n = n(n -3)/2
Multiply by 2/n to get ...
2 = n -3
5 = n . . . . . add 3.
The polygon is a pentagon.
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The sum of interior angles of an n-sided polygon is ...
(n -2)·180°
So, for n=5, the sum of interior angles is ...
(5 -2)·180° = 540° . . . sum of interior angles
