Question

The interior angles of a polygon are in A.P. If the smallest angle be 120' and the
common difference be 5º, then the number of sides is
(A) 8
(B) 10
(C) 9
(D) 6​

Answer 1

Answer:

Step-by-step explanation:

a=120

d=5

sum of n interior angles=n-2(180)

n/2(2a+(n-1)d)=n-2(180)

n(2a+(n-1)d)=2n-4(180)

n(240+(n-1)5)=(2n-4)180

240n+5n^2-5n=360n-540

5n^2-5n=80n-540

5n^2-85n+540=0

on we get 9 as ans