Question

(ii)
First term and common difference of an A.P. are 6 and 3
respectively. Find S27​

Answer 1

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

S27 = 27/2 (2(6) + (27-1)3)

= 27/2 (12+(26)3)

= 27/2 (12+78)

=27/2(90)

=27(45)

S27 = 1215