Cách làm cho bạn:
a) $\frac{7}{x - 3}$ - $\frac{4}{3 - x}$ = $\frac{7}{x - 3}$ + $\frac{4}{x - 3}$ = $\frac{11}{x - 3}$;
b) $\frac{3}{x + 5}$ - $\frac{2}{x + 2}$ = $\frac{3(x + 2)}{(x + 5)(x + 2)}$ - $\frac{2(x + 5)}{(x + 2)(x + 5)}$ = $\frac{3x + 6 – 2x – 10}{(x + 5)(x + 2)}$ = $\frac{x - 4}{(x + 5)(x + 2)}$;
c) $\frac{9}{x - 5}$ - $\frac{6}{x^{2} - 25}$ = $\frac{9}{x - 5}$ - $\frac{6}{(x – 5)(x + 5)}$ = $\frac{9(x + 5)}{(x + 5)(x – 5)}$ - $\frac{6}{(x + 5)(x – 5)}$ = $\frac{9x + 39}{(x + 5)(x – 5)}$.
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