### Trouble with Sigma HW?

posted Nov 10, 2011, 6:24 AM by Taryn Delaney   [ updated Nov 10, 2011, 6:41 AM ]
 #8 and #9 are reviews from Algebra 1:  #8 nCr is probability- it's a combination.  Follow the link for a reminder.#9 "!" means factorial.  Follow the link for a reminder.#10, this is a challenge, so I won't take off if you skip it- but you should still try it.  plug in $\sqrt{-1}$ everywhere you see an "i".    Just write it out, you don't have to evaluate (add) it.For example:$\sum_{n=1}^{20} =\left ( \sqrt{-1} \right )^{4*1}+\left ( \sqrt{-1} \right )^{4*2}...$