[tex]ac+bc -c = 1 - \sqrt{3} \ \textless \ =\ \textgreater \ c(a+b) - c = 1 - \sqrt{3} \ \textless \ =\ \textgreater \
c(a+b-1) = 1 - \sqrt{3} \ \textless \ =\ \textgreater \ c(\sqrt{3}-1) = 1 - \sqrt{3} \ \textless \ =\ \textgreater \
-c(1 - \sqrt{3}) = 1 - \sqrt{3} =\ \textgreater \ c = -1.[/tex]