(1)ab(x+y)(x-y)-xy(a+b)(a-b) (2)x^4+x^2-2ax+1-a^2 (3)a^4-a^2+4a-4

ab(x+y)(x-y)-xy(a+b)(a-b)=ab(x^2-y^2)-xy(a^2-b^2)=abx^2-aby^2-xya^2+xyb^2=ax(bx-ay)-by(ay-bx)=ax(bx-ay)+by(bx-ay)=(ax+by)(bx-ay)x^4+x^2-2ax+1-a^2=x^4+2x^2+1-(x^2-2ax+a^2)=(x^2+1)^2-(x-a)^2=(x^2+1+x-a)...