\(\left(x^2+1\right)-4x\left(1-x^2\right)\)
\(=\left(x^2+1\right)+4x\left(x^2+1\right)\)
\(=\left(x^2+1\right)\left(1+4x\right)\)
\(\left(x^2+1\right)-4x\left(1-x^2\right)\)
\(=\left(x^2+1\right)-4x\left(x^2+1\right)\)
\(=\left(x^2+1\right)\left(1-4x\right)\)