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$\text{a)}$
$\text{f(x) = $-x^{5}$ - $7x^{4}$ - $2x^{3}$ + $x^{2}$ + 4x + 9}$
$\text{g(x) = $x^{5}$ + $7x^{4}$ + $2x^{3}$ + $4x^{2}$ + 6x - 9}$
$\text{b) h(x) = f(x) + g(x)}$
$\text{h(x) = $-x^{5}$ - $7x^{4}$ - $2x^{3}$ + $x^{2}$ + 4x + 9 + $x^{5}$ + $7x^{4}$ + $2x^{3}$ + $4x^{2}$ + 6x - 9}$
$\text{h(x) = $5x^{2}$ + 10x}$
$\text{Vậy h(x) = $5x^{2}$ + 10x}$
$\text{c) Cho  h(x) = $5x^{2}$ + 10x = 0}$
$\text{h(x) = 5x(x + 2) = 0}$
$\text{=> \(\left[ \begin{array}{l}x = 0\\x + 2 = 0\end{array} \right.\) }$
$\text{=> \(\left[ \begin{array}{l}x = 0\\x = -2\end{array} \right.\)}$
$\text{Vậy nghiệm của h(x) là x = 0 và x = -2.}$