(a^2+b^2-c^2)^2-4a^2b^2 =(a^2+b^2-c^2)^2-(2ab)^2 =(a^2+b^2-c^2+2ab)(a^2+b^2-c^2-2ab) =[(a+b)^2-c^2][(a-b)^2-c^2] =(a+b+c)(a+b-c)(a-b+c)(a-b-c)
