10x^3 y^2 z - 25x^2 y z + 5xy
=5xy(2x^2 y z-5xz+1)
a(x+y)-(a-b)(x+y)
=(x+y)(a-a+b)=b(x+y)
81x^2-25y^2
=(9x-5y)(9x+5y)
6mn^2(2-mn^4/3)+(-mn^3/2)^2
=6mn^2(2-mn^4/3) + m^2n^6/4
=mn^2(12 - 2mn^4 +mn^4/4)
=mn^2(12-7mn^4/4)
若x^2+4x-4=0,x^2+4x=4
则3x^2+12x-5 =3(x^2+4x)-5
=3×4-5=7
(a-b)(a+b)(-a+b)(-a-b)= (a+b)^2(a-b)^2
x^2-10xy+25y^2=(x-5y)^2