(1)+(2+3)+(4+5+6)......n th term, find out the sum of this series upto n th term.
Bikram Saha , 4 Years ago
Grade 11
1 Answers
Aditya Gupta
Last Activity: 4 Years ago
Note that the last number in the bracket of each term (1,3,6,...) is simply the set of triangular numbers. So, in nth bracket, the last term would be n(n+1)/2 [nth triangular number].
Now, the sum of the given series is clearly equal to S= 1+2+3+.....+m where m is the last term of the nth bracket.
So S= m(m+1)/2 (sum of natural numbers)
But m= n(n+1)/2
So substitute this value of m in S to get
S= n(n+1)(n^2+n+2)/8
KINDLY APPROVE :))
Provide a better Answer & Earn Cool Goodies
LIVE ONLINE CLASSES
Prepraring for the competition made easy just by live online class.
Full Live Access
Study Material
Live Doubts Solving
Daily Class Assignments
Ask a Doubt
Get your questions answered by the expert for free