1.7 Lösning 5c
Från Mathonline
\(\begin{align} \lg\,(x+1) + \lg\,(x-1) & = \lg 3 - \lg 4 \; & &: \;\text{Logaritmlag 1 i VL + 2 i HL}\\ \lg\,((x+1) \cdot (x-1)) & = \lg\,\left({3 \over 4}\right) \; & &: \;\text{Konjugatregeln i VL}\\ \lg\,(x^2-1) & = \lg\,\left({3 \over 4}\right) \; & &\;| \;10\,^{\cdot}\\ x^2 - 1 & = {3 \over 4} \\ x^2 & = {3 \over 4} + 1 \\ x^2 & = {7 \over 4} \\ x & = {1 \over 2} \, \sqrt{7} \end{align}\)
