1)a^2(m+n)^3-a^2 b^3
=a^2((m+n)^3- b^3)
=a^2(m+n- b)((m+n)^2+b(m+n)+ b^2)
2)y^2(x^2-2x)^3+y^2
=y^2((x^2-2x)^3+1)
=y^2(x^2-2x+1)((x^2-2x)^2-(x^2-2x)+1)
=y^2(x-1)^2(x^4-4x^3+4x^2-x^2+2x+1)
=y^2(x-1)^2(x^4-4x^3+3x^2+2x+1)
3)a^4 b+a^3 b^2-a^2 b^2-a b^4
=ab(a^3+a^2 b-ab-b^3)
=ab((a-b)(a^2+ab+b^2)+ab(a-b))
=ab(a^2+2ab+b^2)(a-b)
=ab(a+b)^2(a-b)
=a²【(m+n)³+b³】
=a²(m+n+b)【(m+n)²+b²-b(m+n)】
=a²(m+n+b)(m²+n²+b²+2mn-bm-bn)