Question 34411
a) Difference is 2;
b) a(101) = 1+(101-1)(2) = 1+200 = 201;
c) S(20) = 20(1 + 19(2)/2) = 20(1+19) = 400;
d) S(30) = 30(1 + (29)2/2) = 30(30) = 900 
e) Observation : Sum is the same as the square of the number of terms.