（1）x平方-1分之x平方+x-2=(x+2)(x-1)/(x+1)(x-1)=(x+2)/(x+1)（2）3x平方-9x-12分之x平方+2x+1=(x+1)^2/[3(x-4)(x+1)]=(x+1)/3(x-4)（3）x平方-7x+12分之-x平方+9x-20=-(x-4)(x-5)/(x-4)(x-3)=-(x-5)/(x-3)...