Question

The first term of an A.P is 2 and the common difference is 3. Find the sum of the first 11 terms

Answer 1

S11 = 11/2 (2a+10d)

so now plug and chug

Answer 2

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

=11/2[2×2+(11-1)3]
=11/2[4+30]
=11/2×34
=187