How Do You Expand General Summation Formulas?

[psycho2499]

I can never remember how to expand a summation into form: $$\sum$$ⁿ_k=1(2²). Thats just a recent example. I can't remember the expansion form any sort of summation really except when it has a defined upper bound.

 

[Dick]

The upper bound is n and the lower bound is 1 isn't it? Looks to me like 4*n.

 

[psycho2499]

sorry i meant to say 2^n for the eq.

 

[Dick]

Then isn't it n*2^n, or did you mean 2^k? Then it's just a finite geometric sum.

 

[psycho2499]

this is what i get for only half paying attention to what i type. damn finals. 2^k, Sorry bout that

 

[Dick]

Then it's just a dumb little finite geometric sum. http://en.wikipedia.org/wiki/Geometric_progression