In Latex, I used the arrray command to set up multiline equations:
Example: {lcr} means: 3 columns with indentations respectively left, center and right

\begin{array}{lcl} z & = & a \ f(x,y,z) & = & x + y + z \end{array}

To create a system: \begin {cases} equation\equation\end{cases}

To create a horizontal line: (for vertical adding)
\hline

To create the approximation symbol:
\approx{0.979 }

I couldn’t get the array function you used to work, but I found this one, and it seems to be working for me:
\begin{eqnarray}
x &=& 0\
y &=& \frac{1}{2}x+3\
y &=& \frac{1}{2}(\textcolor{blue}{0})+3\
y &=& 0+3\
y &=& 3\
\end{eqnarray}

Here are some other notations I’ve been using a lot:
fraction: \frac{numerator}{denominator}
text color: \textcolor{color}{text} (So, to have a red 3 in the text, you’d put “\textcolor{red}{3}”
?=: \stackrel{?}{=}
not equal: \neq
greater than or equal to: \geq
less than or equal to: \leq