a-b-3ab=0a-b=3aby原式=[2(a-b)+3ab]/[(a-b)-ab]=[2(3ab)+3ab]/[(3ab)-ab]=9ab/2ab=9/2
由已知可得,a-b=3ab,所求的代数式=2(a-b)+3ab/(a-b)-ab=6ab+3ab/3ab-ab=9ab/2ab=9/2
因为a-b-3ab=0, 所以a-b=3ab2a+3ab-2b/a-ab-b=[2*(a-b)+3ab]/[(a-b)-ab]=(6ab+3ab)/(3ab-ab)=9/2