For this example you might also like to look at the "factored form" test. This test is designed to establish if the answer is in factored form and equivalent to the teacher's answer. This test *does* cope with even powers and minus signs under the bracket. It also provides useful feedback for answers like (4*x-8)^2
If you come across other elementary things like this and can't work out how to establish the properties please ask. I'm likely to have already written questions which cover it. In particular, the Demo course distributed with STACK has representative questions covering all the manipulations in http://www.mth.kcl.ac.uk/staff/ad_barnard/Pocket.pdf Tony's "map" is used as a catalog for the questions so you can find them.