a) \(4x^2-20x+25-36y^2\)
\(=\left(4x^2-20x+25\right)-36y^2\)
\(=\left(\left(2x\right)^2-2.2x.5+5^2\right)-\left(6y\right)^2\)
\(=\left(2x-5\right)^2-\left(6y\right)^2\)
\(=\left(2x-5-6y\right)\left(2x-5+6y\right)\)
d) \(x^4+6x^3+9x^2-16\)
\(=x^2\left(x^2+6x+9\right)-16\)
\(=x^2\left(x^2+2x3+3^2\right)-4^2\)
\(=x^2\left(x+3\right)^2-4^2\)
\(=x^2\left(x+3-4\right)\left(x+3+4\right)\)