What is the sum of the first 22 terms of the sequence -62, -15, 32, 79, ... ?

Question

Not sure how to do this?

Answers are either: 878, 9493, 925, 8568 or none

Answer 1

This is an arithmetic sequence with common difference d = 47.

 

a₁ = -62    a₂₂ = a₁ + 21d = -62 + 21(47) = 925

 

S₂₂ = sum of first 22 terms = (22/2)[a₁ + a₂₂] = 11(-62 + 925) = 9493

 

 

 

Answer 2

Lets find the formula.  The common difference is 47, so we know this is arithmetic sequence.  The first term is -62. 

 

The formula is then

 

a_n = -62 + 47(n - 1)

a_n = 47n - 109

 

 

The sum is then

 

a₁ + a₂ + a₃ + .... + a₂₂

 

 

You can use the graphing calculator to find the sum using that formula.