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第61頁

信息發(fā)布者：

解：?$ \frac {x+y}{(x-y)(y-z)}$?

?$ \frac {y+z}{(y-z)(y-x)}=\frac {-y-z}{(x-y)(y-z)}$?

解：?$ \frac 3{9\ \mathrm {m^2}-12m+4}=\frac {6+9m}{(2-3m)^2(2+3m)}$?

?$ \frac 2{4-9\ \mathrm {m^2}}=\frac {4-6m}{(2-3m)^2(2+3m)}$?

解：?$ \frac 1{2x+3}=\frac {2x-3}{(2x+3)2x-3)}$?

?$ \frac 3{3-2x}=\frac {-6x-9}{(2x+3)(2x-3)}$?

?$ \frac {2x+5}{4x^2-9}=\frac {2x+5}{(2x+3)(2x-3)}$?

解：?$ \frac 1{x+1}=\frac {1-x^2}{(1+x)^2(1-x)}$?

?$ \frac {x-1}{x^2+2x+1}=\frac {-x^2+2x-1}{(1+x)^2(1-x)}$?

?$ \frac 1{1-x}=\frac {x^2+2x+1}{(1+x)^2(1-x)}$?

解：?$a=x-1，$?最簡(jiǎn)公分母?$b=3(x+1)(x-1)$?

∴?$\frac ba=\frac {3(x+1)(x-1)}{x-1}=3(x+1)=3$?

即：?$x=0$?

∴?$\frac 1{3x^2-3}=-\frac 13$?

?$ \frac 2{x-1}=-2$?

解： ∵?$\frac 1x-\frac 1y=2$?

∴等式兩邊同時(shí)乘?$xy，$?得：?$x-y=-2xy$?

∴原式?$=\frac {-2xy+4xy}{2×(-2xy)-xy}=-\frac 25$?

解：由題意得，平均速度為?$\frac {2s}{\frac s{v_1}+\frac s{v_2}}=\frac {2v_1v_2}{v_1+v_2}(\ \mathrm {m/s})$?

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