Problem 599

 

Find the sum.

1 + 6 + 11+ ……+(5n – 4)

 

Solution :-

 

We are given an arithmetic sequence. The first last terms of this sequence are a₁ = 1

and  a_n = 5n – 4.

To find the sum of the given sequence, use the formula S_n = .

S_n = . (Substitute a₁ = 1 and a_n = 5n – 4.)

S_n = .