diff --git a/analyse/exercices/main.tex b/analyse/exercices/main.tex index cfcb7d0..37849c1 100644 --- a/analyse/exercices/main.tex +++ b/analyse/exercices/main.tex @@ -206,6 +206,79 @@ \paragraph{$(E_5)$} $y'' - 7y' + 10 y = (x + 3) e^{2x}$ + \begin{enumerate}[label=\alph*)] + + \item Solution homogène + \begin{align*} + r^2 - 7r + 10 = 0 + \implies \Delta = 9 + \implies + \left\{ + \begin{array}{l} + r_1 = \frac{7 - 3}{2} = 2 \\\\ + r_2 = \frac{7 + 3}{2} = 5 \\ + \end{array} + \right. + \end{align*} + \begin{align*} + \implies + y_0 = \lambda e^{2x} + \mu e^{5x} + \end{align*} + + \item Solution particulière + + Second membre~: $(x + 3)e^{\alpha x}$ avec $\alpha = 2$ $\implies \alpha$ racine de l'équation caractéristique. + \begin{align*} + &\left\{ + \begin{array}{l} + y_1 = xe^{2x} (ax + b) \\ + y_1' = (2x + 1)e^{2x}(ax + b) + axe^{2x} \\ + y_1'' = (4ax + 2a + 2b)e^{2x} + (4ax^2 + 4ax + 4bx + 2b)e^{2x} \\ + \end{array} + \right. \\ + \implies + &\left\{ + \begin{array}{l} + y_1 = xe^{2x} (ax + b) \\ + y_1' = (2ax^2 + 2ax + 2bx + b)e^{2x} \\ + y_1'' = (4ax^2 + 8ax + 4bx + 2a + 4b)e^{2x} \\ + \end{array} + \right. + \end{align*} + + Dans $(E_5)$~: + + $(4ax^2 + 8ax + 4bx + 2a + 4b)e^{2x} - 7(2ax^2 + 2ax + 2bx + b)e^{2x} + 10(ax + b)xe^{2x} = (x + 3) e^{2x}$ + \begin{align*} + \implies + -6ax + 2a - 3b = x + 3 + \implies + \left\{ + \begin{array}{l} + -6a = 1 \\ + 2a - 3b = 3 \\ + \end{array} + \right. + \implies + \left\{ + \begin{array}{l} + a = \frac{-1}{6} \\\\ + b = \frac{-10}{9} \\ + \end{array} + \right. + \end{align*} + \begin{align*} + \implies + y_1 = xe^{2x}(-\frac{1}{6}x - \frac{10}{9}) + \end{align*} + + \item Solution générale + \begin{equation*} + y = y_0 + y_1 = \boxed{\lambda e^{2x} + \mu e^{5x} + xe^{2x}(-\frac{1}{6}x - \frac{10}{9})} + \end{equation*} + + \end{enumerate} + \paragraph{$(E_6)$} $y'' - y = x^3$