Simplificar: $E = \frac{1 + m \text{sen}(x-y) - \cos(x-y)}{m + \text{sen}(x-y) + m \cos(x-y)}$, conociendo que:
$$ \begin{cases} \text{sen } x - \text{sen } y = m \\ \cos x + \cos y = n \end{cases} $$