你好,小巷老梧桐

∵a-b-3ab=0
∴a-b=3ab
∴(a-b-6ab)/(2a-2b+3ab)
=[(a-b)-6ab)]/[2(a-b)+3ab]
=[3ab-6ab]/[6ab+3ab]
=(-3ab)/9ab
=-1/3