X=1/X,X^2=1,X=±1,
(x²+2x-3)/(x-1)•(x²-3x+1)/(x+3)
=(X+3)(X-1)/(X-1)*(X^2-3X+1)/(X+3)
=X^2-3X+1.
=2-3X
当X=1时,原式=-1,
当X=-1时,原式=5.=X^2-3X+1。=2-3X这一步怎么变得由已知：X^2=1,∴X^2-3X+1。=2-3X