Question

n n If S???? ∑ a???? = 1/6 n (2n² + 9n + 13), then ∑ √a????, equals r =1 r =1 (a) n (n+1)/2 (b) n (n+2)/2
(c) n (n+3)/2 (d) n (n+5)/2

Answer 1

a

4

−a

2

+16

a

2

+16=0

a

2

=−16

a=4