JEE Main 2016 Mathematics question
The sum , is equal to:
Answer: (2)
Solution
The trick is to split the summand into a telescoping difference. Observe that
r·(r+1)! - (r-1)· r! = r![r(r+1) - (r-1)] = r!+r-r+1] = +1)r!
exactly as require
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