[tex]\dfrac{1-\sqrt 5}{1+\sqrt 5}\\\\\\=\dfrac{\left( 1- \sqrt 5\right)\left( 1- \sqrt 5\right)}{\left( 1+ \sqrt 5\right)\left( 1- \sqrt 5\right)}\\\\\\=\dfrac{\left( 1-\sqrt 5)^2}{1^2 - \left(\sqrt 5 \right)^2}\\\\\\=\dfrac{1+\left(\sqrt 5 \right)^2 -2 \sqrt 5\cdot 1}{1-5}\\\\\\=\dfrac{1+5-2\sqrt 5}{-4}\\\\\\=-\dfrac{6-2\sqrt 5}{4}\\\\\\=-\dfrac{2\left(3-\sqrt 5 \right)}{4}\\\\\\=-\dfrac{3-\sqrt 5}{ 2}\\\\\\=\dfrac{\sqrt 5 -3}{2}[/tex]
