
Couple binomial Things
First, can some tell me if I did this right, and if not, tell me what I did wrong.
expand (x+4y)^5
I got: x^5 + 20x^4y + 26x^3y^2 + 74x^2y^3 + 261xy^4 + 1024y^5
Second, I've forgotten the formulas for exponential growth and decay, If someone could provide those I'd greatly appreciate it.

using the binomial formula:
$\displaystyle
\begin{gathered}
\left( {x + 4y} \right)^5 = \sum\limits_{k = 0}^5 {\left( {\begin{array}{*{20}c}
5 \\
k \\
\end{array} } \right)} x^{5  k} \left( {4y} \right)^k \hfill \\
\hfill \\
where:\quad \left( {\begin{array}{*{20}c}
5 \\
k \\
\end{array} } \right) = \frac{{5!}}
{{k!\left( {5  k} \right)!}}\quad \hfill \\
\end{gathered}
$

ummm
I used Pascal's triangle, I was wondering if my numerical coefficients are correct mostly, what you said went over my head, thanks for trying to help me anyways :) and still looking for exponential growth and decay formulas, they have something to do with halflife I think.
