deletions | additions       diff --git a/introduction.tex b/introduction.tex  index 4606050..59554f5 100644  --- a/introduction.tex  +++ b/introduction.tex 
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[ A_{m} cos ( k_x x) + B_{m} sin ( k_x x) ]  [ C_{n} cos ( k_y y) + D_{n} sin ( k_y y) ]  \end{equation}  Calculando as segundas  derivadas cruzadas de $h(x,y,z)$ em relação $x, y$ e $z$  temos : \begin{equation}  \frac{\partial^2 h(x,y,z) }{\partial x \partial y} =   \sum^{\infty}_{n=0} \sum^{\infty}_{m=0} exp \{ - (k_x^2 +k_y^2)^{1/2} z \}