Lösung 2.1:3b

If we take out the factor 5, we see that the expression can be factorized using the conjugate rule

\displaystyle \qquad \begin{align} 5x^2-20&=5(x^4-4)\\ &= 5(x^2-2^2)\\ &= 5(x+2)(x-2) \end{align}