Cách làm cho bạn:
a) $\frac{x-1}{x^{3}+1}$ ; $\frac{2x}{x^{2}-x+1}$; $\frac{2}{x+1}$
Ta có: $\frac{x-1}{x^{3}+1}=\frac{x-1}{(x+1)(x^{2}-x+1)}$
MTC là $(x+1)(x^{2}-x+1)$
Suy ra: $\frac{x-1}{x^{3}+1}=\frac{x-1}{(x+1)(x^{2}-x+1)}$
$\frac{2x}{x^{2}-x+1}=\frac{2x(x+1)}{(x+1)(x^{2}-x+1)}$
$\frac{2}{x+1}=\frac{2(x^{2}-x+1)}{(x+1)(x^{2}-x+1)}$
b) $\frac{x+y}{x(y-z)^{2}}$; $\frac{y}{x^{2}(y-z)^{2}}$; $\frac{z}{x^{2}}$
Ta có: MTC là $x^{2}(y-z)^{2}$
Suy ra: $\frac{x+y}{x(y-z)^{2}}=\frac{(x+y)x}{x^{2}(y-z)^{2}}$
$\frac{y}{x^{2}(y-z)^{2}}$
$\frac{z}{x^{2}}=\frac{z(y-z)^{2}}{x^{2}(y-z)^{2}}$
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