[Tex/LaTex] How to subtract two equations

alignequations

I am trying to subtract one equation from another but I can't get it to display the way that I want. This is what I have right now.

\begin{align*}
&y&=2x+5\\   
-&&\\    
&y&=3x+10\\\hline   
&0&=-x-5    
\end{align*}

Best Answer

This does not look very good but seems close to what your code is attempting to do, where I use \cline{} to draw the horizontal line, and \phantom{y=} to push the minus sign to the left

enter image description here

Recomended Solution:

However, I would suggest the use of \intertext or \shortintertext from the mathtools package, and refer to the equations:

enter image description here

Notes:

Requires two runs: first run will display a (??) in the cross reference.
\shortintertext yields better spacing but requires an additional package. Alternatively, you can use \intertext which is available in amsmath.
The mathtools package already includes amsmath.

Code:

\documentclass{article}
\usepackage{amsmath}
\begin{document}
\begin{align*}
    y&=2x+5\\   
    -\phantom{y=}&\\    
    y&=3x+10\\
   \cline{1-2}
    0&=-x-5    
\end{align*}
\end{document}

\documentclass{article}
\usepackage{mathtools}
\begin{document}
\begin{align}
    y&=2x+5 \label{eqn:one}\\
    y&=3x+10 \label{eqn:two}\\
  \shortintertext{Subtracting \eqref{eqn:two} from \eqref{eqn:one} yields}
    0&=-x-5  \notag
\end{align}
\end{document}

Related Solutions

[Tex/LaTex] Number equations and preserving alignment of equal signs

Here is a small sample of numbering equations.

\documentclass[12pt]{article}

\usepackage{amsmath}

\begin{document}

\begin{align} % numbers equations automatically
x &= (1-x) + 2x \\ % \\ ends the line
&= (x+y) - y \nonumber \\ % \nonumber removes the equation number 
&= \frac{x}{2} + \frac{x}{2} % last line does not have \\ 
\end{align}

\begin{align*} % use of * removes all numbers in this block
x &= (2x + 5) - (x+5) \\
&= yx - (y-1) x 
\end{align*}

\end{document}

This sample produces

[Tex/LaTex] Center text between two lines of equation

You can lower manually the clause:

\documentclass{article}
\usepackage{amsmath}

\begin{document}

\begin{equation}
\label{eq:distrib}
\begin{alignedat}{2}
n_c    &= \max[N \cdot z_{\max} \cdot x, 2 \cdot n_{\min}]
&\quad&\raisebox{-.5\normalbaselineskip}[0pt][0pt]{%
    where $x\sim U([0,1])$%
} \\
n_{co} &= \min[\max[n_c \cdot x, n_{\min}], n_c - n_{\min}] \\
n_{cp} &= n_c - n_{co} \\
n_f    &= N - n_c
\end{alignedat}
\end{equation}

\end{document}

I used \max and \min (you should, too). I also removed all \left and \right tokens, which only do evil here.

I'd also suppress all \cdot symbols, which are very seldom used to denote multiplication in professional math.

However, my feeling is that the clause about x should be moved in the text following the display.