Prove that $E_{n+1}= F_nA + F_{n+1}B$ We have the following definitions
$E_0 =A, E_1=B,$
$ E_{n+2} = E_{n+1} +E_n$, for $n \geq 0$
This is my scratch work
$E_0=A, E_1 = B, E_2= A+B, E_3= A +2B, E_4= 2A+3B, E_5= 3A +5B, E_6= 5A + 8B...$
Noticing that the coefficients of these equations are the Fibonacci numbers we can directly see that
$E_{n+1}= F_nA + F_{n+1}B$
Is this a good enough proof? I realized I didn't use this relation $ E_{n+2} = E_{n+1} +E_n$, but I did not see it necessary.
 A: Induction is really the easiest route:
Just sum
$\quad E_{n}= F_{n-1}A + F_{n}B$
$\quad E_{n+1}= F_nA + F_{n+1}B$
to get 
$\quad E_{n+2}= F_{n+1}A + F_{n+2}B$
A: Here is a formal derivation of your result. The sequence you have found is a generalization of the Fibonacci sequence.
There have been many extensions of the sequence with adjustable (integer) coefficients and different (integer) initial conditions, e.g., $f_n=af_{n-1}+bf_{n-2}$. (You can look up Pell, Jacobsthal, Lucas, Pell-Lucas,  and Jacobsthal-Lucas sequences.) Maynard has extended the analysis to $a,b\in\mathbb{R}$, (Ref: Maynard, P. (2008), “Generalised Binet Formulae,” $Applied \ Probability \ Trust$; available at http://ms.appliedprobability.org/data/files/Articles%2040/40-3-2.pdf.)
We have extended Maynard's analysis to include arbitrary $f_0,f_1\in\mathbb{R}$. It is relatively straightforward to show that
$$f_n=\left(f_1-\frac{af_0}{2}\right) \frac{\alpha^n-\beta^n}{\alpha-\beta}+\frac{f_0}{2} (\alpha^n+\beta^n) $$
where $\alpha,\beta=(a\pm\sqrt{a^2+4b})/2$.
The result is written in this form to underscore that it is the sum of a Fibonacci-type and Lucas-type Binet-like terms. It will also reduce to the standard Fibonacci and Lucas sequences for $a=b=1 \ \text{and} \ f_0=0, f_1=1$.
So, specializing to your case, we can say
$$E_n=\left(B-\frac{A}{2} \right)F_n+\frac{A}{2}L_n$$
where
$$F_n,L_n=\frac{\varphi^n \mp \psi^n}{\varphi \mp \psi}\\
\varphi,\psi=(1\pm \sqrt{5})/2
$$
Ergo,
$$
E_n=BF_n+\frac{A}{2}(L_n-F_n)=AF_{n-1}+BF_n
$$
since $L_n-F_n=2F_{n-1}$.
This proves the OP's assertion.
