第78页 - 江苏版启东中学作业本八年级数学（上下册）

D

x

$\frac {1}{x-1}$

$\frac {k+1}{k-1}$

$=\frac {x+4-1}{x²+3x}$

$=\frac {x+3}{x(x+3)}$

$=\frac {1}{x}$

$=\frac {x-3+1-1+x}{x-3}$

$=\frac {2x-3}{x-3}$

$=\frac {x+1}{(x+1)(x-1)}+\frac {x²-3x}{(x+1)(x-1)}$

$= \frac {x²-2x+1}{(x+1)(x-1)}$

$=\frac {(x-1)²}{(x+1)(x-1)}$

$=\frac {x-1}{x+1}$

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

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

$=\frac {2x^2-x^2+y^2}{x+y}$

$=\frac {x^2+y^2}{x+y}$

互为相反数

1

2