(a^2+b^2-c^2)-4a^2b^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)