The number of diagonals in a certain regular polygon is equal to ten times the number of sides. How many sides does this polygon have?
Number of diagonals of a polygon n ( n-3)/2
n(n-3)/2 = 10n
n^2 -3n = 20n
n^2 -23n= 0
n ( n- 23) = 0 n = 0 (throw out) or n = 23