Question

Find the sum of n terms of an A.P.whose nth terms is given by an= 5 - 6n.

Answer 1

We have, an = 5-6n
⇒ a₁ = 5 - 6 x 1 = -1
So, the given sequence is an A.P with first term a = a₁ = -1 and last term l = a_n = 5 - 6n
Therefore the sum of n terms is given by: S_n= n/2 (a+l)= n/2 (-1+5-6n)=2n-3n²