1. 分式$\frac{1}{xy}$、$\frac{2}{yz}$、$\frac{4}{xz^{2}}$的最简公分母是______.

$xyz^{2}$

2. 分式$\frac{y}{2x^{5}}$和$\frac{y}{5x^{2}}$的最简公分母是( )
A. $10x^{7}$
B. $7x^{10}$
C. $10x^{5}$
D. $7x^{7}$

C

3. 通分：
(1) $\frac{x}{ab}$，$\frac{y}{bc}$； (2) $\frac{z}{x^{2}y}$，$\frac{x}{y^{2}z}$；
(3) $\frac{5}{8xy^{2}}$，$\frac{y}{3x^{2}}$； (4) $\frac{2}{xy^{2}}$，$\frac{3}{2xy}$，$\frac{1}{5x^{2}y}$.

(1) $\frac{x}{ab}=\frac{xc}{abc},\frac{y}{bc}=\frac{ay}{abc}$; (2) $\frac{z}{x^{2}y}=\frac{yz^{2}}{x^{2}y^{2}z},\frac{x}{y^{2}z}=\frac{x^{3}}{x^{2}y^{2}z}$; (3) $\frac{5}{8xy^{2}}=\frac{15x}{24x^{2}y^{2}},\frac{y}{3x^{2}}=\frac{8y^{3}}{24x^{2}y^{2}}$; (4) $\frac{2}{xy^{2}}=\frac{20x}{10x^{2}y^{2}},\frac{3}{2xy}=\frac{15xy}{10x^{2}y^{2}},\frac{1}{5x^{2}y}=\frac{2y}{10x^{2}y^{2}}$

4. 通分：
(1) $\frac{1}{2(x + 1)}$，$\frac{x}{3(x + 1)}$； (2) $\frac{a}{a + 2}$，$\frac{1}{(a + 2)^{2}}$；
(3) $\frac{x}{x + 2}$，$\frac{3}{x^{2} - 4}$； (4) $\frac{2}{x + 1}$，$\frac{x}{x^{2} + 2x + 1}$.

(1) $\frac{1}{2(x + 1)}=\frac{3}{6(x + 1)},\frac{x}{3(x + 1)}=\frac{2x}{6(x + 1)}$; (2) $\frac{a}{a + 2}=\frac{a(a + 2)}{(a + 2)^{2}},\frac{1}{(a + 2)^{2}}=\frac{1}{(a + 2)^{2}}$; (3) $\frac{x}{x + 2}=\frac{x(x - 2)}{(x + 2)(x - 2)},\frac{3}{x^{2}-4}=\frac{3}{(x + 2)(x - 2)}$; (4) $\frac{2}{x + 1}=\frac{2(x + 1)}{(x + 1)^{2}},\frac{x}{x^{2}+2x + 1}=\frac{x}{(x + 1)^{2}}$