TeX Quellcode:

\begin{array}{rcl}f\left(-2+\sqrt{20}\right) &=& \sqrt[4]{\left(-2+\sqrt{20}\right)^2+4\left(-2+\sqrt{20}\right)}-1\\&=& \sqrt[4]{4+20-4\sqrt{20}-8+4\sqrt{20}}-1\\&=& \sqrt[4]{16}-1\\&=& 2-1\\&=& 1\\\end{array}