Cách làm cho bạn:
a) $\frac{3}{2x + 6}$ - $\frac{x – 6}{2x^{2} + 6x}$ = $\frac{3}{2(x + 3)}$ - $\frac{x - 6}{2x(x + 3)}$ = $\frac{3x}{2x(x + 3)}$ - $\frac{x - 6}{2x(x + 3)}$ = $\frac{3x – x + 6}{2x(x + 3)}$ = $\frac{2x + 6}{2x(x + 3)}$ = $\frac{1}{x}$;
b) x^{2} + 1 - $\frac{x^{4} – 3x^{2} + 2}{x^{2} - 1}$ = $\frac{(x^{2} + 1)(x^{2} – 1)}{x^{2} - 1}$ - $\frac{x^{4} – 3x^{2} + 2}{x^{2} - 1}$ = $\frac{x^{4} – 1 – (x^{4} – 3x^{2} + 2)}{x^{2} - 1}$ = $\frac{3x^{2} - 3}{x^{2} - 1}$ = 3.
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