(5a-2b+3c)^2-(2a-4b+3a)^2
=[(5a-2b+3c)+(2a-4b+3a)][(5a-2b+3c)-(2a-4b+3a)]
=(5a-2b+3c+2a-4b+3a）（5a-2b+3c-2a+4b-3a)
=(10a-6b+3c)(2b+3c)