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