sophietrophy wrote:

blueseas wrote:

alphabeta1234 wrote:

What is the sum of series S? Is there a shortcut/formula? I understand you can evaluate and sum each expression but I am trying to find a better solution.

S=1^3+2^3+3^3+4^3+5^3+6^3+7^3

Is there a general formula for S(k,a)=Sum(a^k)?

Hi,

i think there will be no need of these types of formulas in GMAT,BUT STILL HERE IT IS:

S=\(1^3+2^3+3^3+4^3+5^3+6^3+7^3+......+n^3\)\(=\) \((n(n+1)/2)^2\)

hope it helps

This was great!

How would you recommend doing this, though? Just by solving it out?

i would recommend to learn the formula in order to save time.

few more formulas are below.

The sum of first n natural numbers = \(n(n+1)/2\)

The sum of squares of first n natural numbers is \(n(n+1)(2n+1)/6\)

The sum of cubes of first n natural numbers is\((n(n+1)/2)^2/4\)

The sum of first n even numbers= \(n (n+1)\)

The sum of first n odd numbers= \(n^2\)

hope it helps

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