Question

Find the sum of the first 90 terms of the sequence –4, –1, 2, 5, 8, ...

Answer 1

Answer:

d.

11655

Step-by-step explanation:

Answer 2

Answer:

Answer: Sum of first 90 terms is Option d. 11655

Step-by-step explanation:

We have to find the sum of first 90 terms of the sequence -4,-1,2,5,8......

First we find the 90th term of the sequence

As we know the formula A(n)= A(1)+(n-1)d

Given from the sequence

A(1) = (-4)

n=90

d = 3

So A(n) = -4+(90-1)3

            = (-4)+89×3

            = 263

Now we know formula for the sum of any sequence is

Sum S(n) = $\frac{n}{2}(A(1)+A(n))$

Now we know n= 90

A(1) = -4

A(n) =263

Now we put the value in the formula

S(n)= $\frac{90}{2}(-4+263)$

     = 45×259

     = 11655