# Thread: help with binomal question

1. ## help with binomal question

I dont know how to do the signals so ill right in words everything....

(1-1)^n = n SIGMA k=0 nCk * 1^k *(-1)^(n-k)

why does it equals to:
n SIGMA k=0 nCk * (-1)^k

i dont understand why (-1)^(n-k) become (-1)^k

someone can help me please???

2. The following expansion can be written in two ways.
Note the placement of the exponents in the equivalent sums.
$\left( {a + b} \right)^n = \sum\limits_{k = 0}^n {{n \choose k}\left( a \right)^k \left( b \right)^{n - k} } \;\text{OR} \,\sum\limits_{k = 0}^n {{n \choose k}\left( a \right)^{n - k} \left( b \right)^k }$