What are good programs for writing expressions?

By writing expressions, I mean intermediate expressions to "show your work," such as the ones in the below image. LaTex would seem like overkill for such problems. • LaTeX. If you don't want to use your normal word processor, use LaTeX. – Johanna Jan 10 '15 at 2:20
• $\LaTeX$ is a big beauty – janmarqz Jan 10 '15 at 2:41
• LaTeX is both a markup language and a program (which converts that markup language into something like PDF). I get the argument that LaTeX the program seems like overkill for this task (though I don't generally agree with it), but LaTeX the markup language is perfectly suited. I presume this question is asking about the program, rather than the markup language. – David Z Jan 10 '15 at 5:20

I still think LaTeX is the way to go. Once you start having to write several mathematical expressions, any kind of mouse-driven system for specifying them is going to become very frustrating. LaTeX is extremely efficient for doing exactly what you want to do.

\begin{align*}
c_1x + a     &= c_2 x + b \\
c_1x + a - a &= c_2x + b - a\\
c_1x         &= c_2x + b - a \\
c_1x - c_2 x &= c_2x + b - a - c_2 x \\
c_1x - c_2 x &= b - a \\
x            &= \frac{b-a}{c_1 - c_2}
\end{align*}


\begin{align*} c_1x + a &= c_2 x + b \\ c_1x + a - a &= c_2x + b - a\\ c_1x &= c_2x + b - a \\ c_1x - c_2 x &= c_2x + b - a - c_2 x \\ c_1x - c_2 x &= b - a \\ x &= \frac{b-a}{c_1-c_2} \end{align*}

See Getting started with LaTeX for some pointers.