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Sir please help me solve this problem. (ATTACHED). I do not know the summesion of factorial and how to solve the summesion of product of an expression with a factorial.

Sir please help me solve this problem. (ATTACHED).
I do not know the summesion of factorial and how to solve the summesion of product of an expression with a factorial.
 

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Grade:12th pass

1 Answers

Aditya Gupta
2081 Points
5 years ago
rth term is (r^2 – r+1)*r! = [(r+1)^2 – 3r]*r!= (r+1)*(r+1)! – r*r! – 2[(r+1)! – r!]
now obviously (r+1)*(r+1)! – r*r! telescopes and (r+1)! – r! telescopes too! note that here we have used the following property of factorials:
(k+1)!= (k+1)*k!

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