1: \(=4x\left(x-2\right)\)
2: \(=\left(x-4\right)\left(x+4\right)\)
3: \(=\left(5-x-1\right)\left(5+x+1\right)=\left(6+x\right)\left(4-x\right)\)
4: \(=\left(y-2-3\right)\left(y-2+3\right)=\left(y-5\right)\left(y+1\right)\)
5: \(=\left(x-4\right)\left(x^2+4x+16\right)\)