Question

If a polygon has 189 diagonals how many sides does the polygon have ?

Answer 1

(n take 2) minus n = 189
n(n-3)/2 = 189
n(n-3) = 378
n^2-3n-378 = 0
n=21

Answer 2

n(n-3)/2=189
n(n-3)=378
n^2-3n-378=0
n=21