Laurenso
I have an expression `x^2 - a x - b x + ab`. Now I want to substitute `a = 1` and `b = 2` to get `x^2 - x - 2x + 2`. How can I get the result?
```
\documentclass[12pt,a4paper]{article}
\usepackage{mathtools}
\usepackage{amsthm}
\usepackage{calc}
\begin{document}
\pgfmathsetmacro{\a}{1}
\pgfmathsetmacro{\b}{2}
x^2 - \a*x - \b*x + \a*\b
\end{document}
```
I can not get the result `x^2 - x - 2x + 2`.
Top Answer
samcarter
You could wrap your coefficients into a macro to evaluate them:
```
\documentclass{article}
\usepackage{pgf}
\pgfkeys{/pgf/number format/print sign=true}
\newcommand{\foo}[1]{%
\pgfmathparse{#1}%
\pgfmathprintnumber{\pgfmathresult}
}
\begin{document}
\pgfmathsetmacro{\a}{1}
\pgfmathsetmacro{\b}{2}
\[
x^2 \foo{-\a}x \foo{-\b}x \foo{+\a*\b}
\]
\end{document}
```
![Screenshot 2023-07-23 at 15.12.35.png](/image?hash=aea97c022dc5f2225b8df4a44e75f78f4f321c04aefecfbdc2ce744eea34fc9d)