x_1' = -x_1 \
x_2' = x_2

\begin{pmatrix} x_1' \ x_2' \end{pmatrix} = \begin{pmatrix} -1 & 0 \ 0 & 1 \end{pmatrix} \cdot \begin{pmatrix} x_1 \ x_2 \end{pmatrix}

X = (2, 1)
X': ((-x(X)) | y(X))
f = Segment(X, X')
Text1: "\vec{x} = \begin{pmatrix} " + (LaTeX[x(X)]) + " \\ " + (LaTeX[y(X)]) + " \end{pmatrix}"
Text2: "\vec{x}' = \begin{pmatrix} " + (LaTeX[x(X')]) + "  \\  " + (LaTeX[y(X')]) + " \end{pmatrix}"