1)
\(=5\left(a^2-b^2\right)=5\left(a-b\right)\left(a+b\right)\)
2)
\(=2\left(x^4-16\right)=2\left(\left(x^2\right)^2-4^2\right)=2\left(x^2-4\right)\left(x^2+4\right)\)
3)
\(=x^2\left(x^2-4x+4\right)=x^2\left(x-2\right)^2=x.x.\left(x-2\right)\left(x-2\right)\)
4)
\(=x^2\left(x-1\right)-\left(x-1\right)=\left(x^2-1\right)\left(x-1\right)=\left(x-1\right)\left(x+1\right)\left(x-1\right)\)