1.原式=(x-y)[2(x-y)-3]-2
=2（x-y)(x-y)-3(x-y)-2
=(2x-2y+1)(x-y-2)
2..a^2+b^2+c^2-2ab-2bc+2ac
=（a-b+c)^2=[a-(b-c)}^2=a^2-2a*(b-c)+(b-c)^2=a^2-2ab+2ac+b^2-2bc+c^2=a^2-2a*(b-c)+(b-c)^2=（a-b+c)^2
3.2x^4y^2-4x^3y^2+10xy^4=2xy^2(x^3-2x^2+5y^2).