4. Find the sum of the first eighteen terms of the arithmetic sequence whose nth term is an = 15 + 8n.
a. 1438
b. 1638
c. 1836
d. 1783

The sum of first eighteen terms of the arithmetic sequence is

Option B is correct option.

Step-by-step explanation:

We need to find the sum of the first eighteen terms of the arithmetic sequence whose nth  term is an = 15 + 8n

The formula used to calculate sum of arithmetic sequence is:

Finding a₁ by putting n=1

We have

Finding 18th term n=18

So, the sum of first eighteen terms of the arithmetic sequence is:

So, the sum of first eighteen terms of the arithmetic sequence is

Option B is correct option.

i think the answer is b