Question

Find the sum of the first 90 terms of the sequence –4, –1, 2, 5, 8, ... a. 11654 c. 11656 b. 11657 d. 11655

Answer 1

The answer would be D. 11655

Answer 2

Answer: D. 11655

Explanation:

Given sequence : –4, –1, 2, 5, 8, ...

here, the first term = -4

Common difference =
`-4-(-1)=3`

By Arithmetic progression, the sum of n terms will be

`S_(n)=(n)/(2)(2a+(n-1)d)`

Then, the sum of first 90 terms will be

`S_(90)=(90)/(2)(2(-4)+(90-1)(3))=11655`