`\align`

and `\array`

environments.Here's a MWE to show the ugly distribution of equations on a page, that I want to fix.

\documentclass[12pt,letterpaper]{book} \usepackage[T1]{fontenc} \usepackage{amsmath} \usepackage[total={6in,10in},left=1.5in,top=0.5in,includehead,includefoot]{geometry} \begin{document} A small line of text : \begin{align} x &= y^2 - c + d + z^3, & z &= x^3 + x - y^2. \end{align} Just another small line of text : \begin{align} x -5 y + 3 &= y^2, & y^2 &= -\: x^2 + 4 - y^2 - x. \end{align} Yet another line : \begin{align} A + B + E &= b, & B - C &= 0. \end{align} The global distribution of these equations is ugly ! \end{document}

Here's a preview of the compiled code, with some approximate reference lines :

The red line is (approximately) the middle of the text. The blue lines are (approximately) the middle of the left and right parts. I want to "force" the equations to be centered on the blue lines.

Any idea about how to achieve what I'm looking for ?