y=∣x²-1∣/(x-1)=∣(x+1)(x-1)∣/(x-1)
当x≦-1时，y=(x+1)(x-1)/(x-1)=x+1;
当-1≦x≦1时，y=-(x+1)(x-1)/(x-1)=-(x+1);
当x≧1时，y=(x+1)(x-1)/(x-1)=x+1.
