+826 The number of diagonals in a certain regular polygon is equal to $2$ times the number of sides. How many sides does this polygon have?
+135 The formula for # of diagonals for a n-sided poligon is \(\frac{n (n - 3)}{2}\). Therefore,
\(\frac{n(n-3)}{2} = 2n\)
\(n^2 - 3n = 4n\)
\(n^2-7n=0\)
\(n(n-7)=0\)
\(n = 0, 7\)
And since there are no 0-sided polygons, the polygon has 7 sides
