Question 881938
The common difference is 9 - 3 = 6. So d = 6


First term: a1 = 3



Sn = n*(a1 + an)/2



Sn = n*(a1 + a1 + (n-1)*d)/2



Sn = n*(2*a1 + (n-1)*d)/2



S26 = 26*(2*a1 + (26-1)*d)/2 ... plug in n = 26



S26 = 26*(2*3 + (26-1)*d)/2 ... plug in a1 = 3



S26 = 26*(2*3 + (26-1)*6)/2 ... plug in d = 6



S26 = <font color="red">2,028</font>



The sum of the first 26 terms is <font color="red">2,028</font>