Which equation should be used to calculate s9 for the arithmetic sequence an=3n-1 o s9=9/2(2+26) o s9= 9/2(4+17) o s9=9/4(2+26) o s9=9/4(4+26)

1. D

2. A

3. C

4. D

5. A

Step-by-step explanation:

Option A is correct.

The equation = .

Explanation:

Sum of the terms of an arithmetic series is given by

,                  ......[1]

where n is the number of terms, is the first term and  is the last term.

Given the formula for nth term in the arithmetic sequence is,

for n =1

for n =9

Then, put these values in equation [1] for n =9;

or

Therefore, the equation is;

first one because it can't have a fraction in it

step-by-step explanation: