Given a sequence of numbers: 1 , 5, 9…….. Find : the 15th term and the sum from first to 15th term.

Question

Given a sequence of numbers: 1 , 5, 9…….. Find : the 15th term and the sum from first to 15th term.

Answer 1

Each term in the sequence can be represented by:

A(n) = 4n-3

So, A(15) = 4(15) - 3 = 57

 

Checking:

1, 5, 9, 13, 17, 21, 25, 29, 33, 37, 41, 45, 49, 53, 57

 

Sum:

(A₁ + A_n)*n/2

Substituting:

(1 + 57) * 15/2

(58)*15/2

29 * 15

435.