n=110 ( 528n(n+1)(n+2) ) is equal to:
- 65
- 130
- 220
- 440
Answer
(2) 130
Solution
1n(n+1)- 1(n+1)(n+2)= (n+2)-nn(n+1)(n+2)= 2n(n+1)(n+2)
1n(n+1)(n+2)= 12 [ 1n(n+1)- 1(n+1)(n+2) ]
n=110 1n(n+1)(n+2)= 12 [ 11 2- 111 12 ] (telescoping)
= 12 66-1132= 65264
Required sum =528 65264=2 65=130
Answer: (2)