Question

If a=1+√7 find the value of -6/a

Answer 1

a = 1 + √7

$\frac{1}{a}=\frac{1}{1+\sqrt7}=\frac{1}{1+\sqrt7}*\frac{\sqrt7 -1}{\sqrt7 - 1}\\\\=\frac{\sqrt7 - 1}{7 - 1}= \frac{\sqrt7 - 1}{6}\\\\ \frac{-6}{a}=-(\sqrt7 - 1)$