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find 1.1!+2.2!+3.3!+............nterms

find


1.1!+2.2!+3.3!+............nterms

Grade:12

1 Answers

Badiuddin askIITians.ismu Expert
148 Points
14 years ago

Dear tejas

S=1.1!+2.2!+3.3!+............nn!

rearrange

S=(2-1)1!  +(3-1) 2! +(4-1) 3!+.......(n+1-1) n!

   =2 1!  -1 1!  +3 2! -1 2! + 4 3 ! -1 3!...............(n+1) n!  - 1 n!

  =2! -1! +3! -2! +4! -3! +..............(n+1)! -n!

   =(n+1)! -1


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