and ; and ; and ;
ab-a-b=0 and a-ab+b=0
-a-b+ab=0 and a+b-ab=0
a+b-ab=0
Simple sense about some common number facts may allow seeing that you may be able to see that if a=b=0, this will work, and if a=b=2, this will also work. Any other ways you see? Try testing any pick for a and find the corresponding value for b. Will the combination also work?