Problem: Let S be the sum of the first nine terms of the sequence, x+a,x2+2a,x3+3a,…. Then S equals:
Answer Choices:
A. x+150a+x+x8
B. 50a−x−1x+x10
C. x+1x9−1+45a
D. x−1x10−x+45a
E. x−1x11−x+45a
Solution:
x+x2+x3+…+x9
S1=1−xx(1−x9)=x−1x10−x
a+2a+3a+…+9a
S2=29(a+9a)=45aS=S1+S2