a) \(a^2b-4ab^2\)
\(=ab\left(a-4b\right)\)
b) \(x^8+4y^4\)
\(=\left(x^4\right)^2+\left(2y^2\right)^2\)
\(=\left(x^4-2y^2\right)\left(x^4+2y^2\right)\)
c) \(x^2-10x-16y^2+25\)
\(=\left(x^2-10x+25\right)-16y^2\)
\(=\left(x-5\right)^2-\left(4y\right)^2\)
\(=\left[\left(x-5\right)+4y\right]\left[\left(x-5\right)-4y\right]\)
\(=\left(x-5+4y\right)\left(x-5-4y\right)\)