The interior angles of a polygon are in AP the smallest angle is 120 degrees. and the common difference is 5 The number of sides of the polygon.

Dear Vivek,

 120 + 125 + 130 ...+ n

S = n[2a + (n-1)d ]/2

180(n-2) = n[2a + (n-1)d ]/2 here, a= 120 and d= 5 solve for n.

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