①15a^(m+2)b+12a^(m+1)b²-3a^m b³=3a^m.b(5a²+4ab-b²)=3a^m.b(a+b)(5a-b)
②a²b²-4ab+4=(ab-2)²
③mn(m-n)-m(m-n)²=m(m-n)[n-(m-n)]=m(m-n)(2n-m)
④2m(m²-16)=2m(m+4)(m-4)