do this sum!!!

1+(2+3)+(3+4+5)+,,,,,,,,,,

4 Answers

âˆž

1057

Ketan Chandak ·2012-01-05 17:03:55

if it is till n terms and 1 bracket is considered as a single term...

first of all first term in the bracket is same as n and no of terms is also n
so nth term=n2(2n+(n-1)1)

therefore it is n/2[3n-1]=3n²2-n2

using summation formulas...

we get n²(n+1)2

How to do this ?

1+(2+3)+(4+5+6)+,,,,upto n brackets,,,,

1057

Ketan Chandak ·2012-01-27 18:49:08

dis is simpler....
last term of the nth bracket is n(n+1)2

we alrdy knw dat sum of first a natural nos is a(a+1)2

jus replace a as n(n+1)2 in the above formula.... :)

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