Déterminer a,b,c et d pour que:

[tex] \frac{3x + 4}{x {}^{2} + 7x + 12 } = \frac{a}{x + 3} + \frac{b}{x + 4} [/tex]
[tex] \frac{x}{(x - 2) {}^{2} } = \frac{a}{x - 2} + { \frac{b}{(x - 2) {}^{2} } }^{} [/tex]
[tex] \frac{2x {}^{2} + x + 5 }{ x { - 1}^{} } = a + \frac{b}{x + 1} + \frac{c}{x - 1} [/tex]
[tex] { \frac{x { {}^{3} - 2x { + 3x + 1}^{} }^{} }{(x + 2) {}^{2}(x {}^{2} { + 4}) ^{} } }^{} = \frac{a}{x + 2} + \frac{b}{(x + 2) {}^{2} } + \frac{cx + d}{x {}^{2} + 4} [/tex]

merci d'avance ​