第78页 - 通城学典课时作业本八年级数学苏科版江苏专版

D

B

$\frac{2y^2}{9x^2}$

$ \frac{81y^{16}}{x^{12}}$

$-\frac{1}{a+b}$

$解：原式=-\frac{5c}{2a^3}$

$ \begin{aligned}解：原式&=\frac{4(a+b)}{5ab}·\frac{15a^2b}{(a+b)(a-b)} \\ &=\frac{12a}{a-b} \\ \end{aligned}$

$ \begin{aligned}解：原式&=\frac{2a^2}{a+4}·\frac{(a+4)(a-4)}{a(a-4)} \\ &=2a \\ \end{aligned}$

$ \begin{aligned}解：原式&=\frac {a+3}{4-a}×\frac {(a-4)^2}{a(a+3)} \\ &=\frac {4-a}a \\ \end{aligned}$