"2A-2B+3AB/A-B-5B"是否为"2A-2B+3AB/A-B-5AB"
∵A-B-4AB=0
∴A-B=4AB
∴2A-2B+3AB/A-B-5AB
=2(A-B)+3AB/(A-B)-5AB
=8AB+3AB/4AB-5AB
=11AB/-AB
=-11