Question 267110
For a convex regular polygon of n sides the sum of all the internal angles is equal to {{{(n-2)*pi}}}. 


To find the no. of sides, 
{{{(n-2)*180 = 1260}}}
{{{n-2 = 1260/180}}}
{{{n-2 = 7}}}
{{{n = 7 + 2 = 9}}}


Hence, the polygon has 9 sides.