Solution 2.1:3b
From Förberedande kurs i matematik 1
If we take out the factor 5, we see that the expression can be factorized using the conjugate rule
| \displaystyle \begin{align}
5x^2-20&=5(x^4-4)\\ &= 5(x^2-2^2)\\ &= 5(x+2)(x-2)\,\textrm{.} \end{align} |
