解：???$(1)\frac {1}{x+1}=\frac {(x+1)(x-1)}{(x+1)2(x-1)}；$??????$\frac {x-1}{x2+2x+1}=\frac {(x-1)2}{(x+1)2(x-1)}$???
???$\frac {1}{x-1}=\frac {(x+1)2}{(x+1)2(x-1)}$???
???$(2)\frac {1}{x-1}=\frac {x(x+1)}{x(x+1)(x-1)}；$??????$\frac {1}{x2-1}=\frac {x}{x(x+1)(x-1)}$???
???$\frac {1}{x2+x}=\frac {x-1}{x(x+1)(x-1)}$???
