GTP - Question in Exercise 2.6 - vector form (\tau , 1)

[jhidalgocarrio]

Hi,
By doing the Exercise 2.6, we got the question of why do you assume the real part of the complex number is equal to 1 at the line:

mathphysics/LaTeX_and_pdfs/Nakahara_GTP-solutions.tex

Line 394 in 1de826f

\left( \begin{matrix} a & b \\ c & d \end{matrix} \right) \left( \begin{matrix} \tau \\ 1 \end{matrix} \right) = \left( \begin{matrix} a\tau + b \\ c \tau + d \end{matrix} \right)

How the

 (\tau, 1)

nomenclature is deduce from the exercise statement?