Math & Science ⇒ How to number first line of an equation???

[ghostanime2001]

Let's say I have a block of equations as i am solving for a given unknown in a problem. How can I only label the first line of the equation with a number like I'm putting my answer sheet into a PDF format whilst still keeping all my equations on the left-hand side? My LaTeX file looks like this:

Code: Select all

\documentclass{report}
\usepackage{amsmath,fullpage,nccmath,graphicx,leqno}
\pagestyle{empty}
\begin{document}
\begin{fleqn}
\begin{align*}
T_{2}\cos\theta_{2}&=T_{1}\cos\theta_{1} \\ 
T_{2}&=\frac{T_{1}\cos\theta_{1}}{\cos\theta_{2}} \\
T_{1}\sin\theta_{1} + \left(\frac{T_{1}\cos\theta_{1}}{\cos\theta_{2}}\right)\sin\theta_{2}&=350 \\
T_{1}\sin\theta_{1} + \frac{T_{1}\cos\theta_{1}\sin\theta_{2}}{\cos\theta_{2}}&=350 \\
T_{1}\sin\theta_{1} + T_{1}\frac{\cos\theta_{1}\sin\theta_{2}}{\cos\theta_{2}}&=350 \\
T_{1}\left(\sin\theta_{1} + \frac{\cos\theta_{1}\sin\theta_{2}}{\cos\theta_{2}}\right)&=350 \\
T_{1}\left(\frac{\sin\theta_{1}\cos\theta_{2}+\cos\theta_{1}\sin\theta_{2}}{\cos\theta_{2}}\right)&=350 \\
T_{1}\left(\frac{\sin\left(\theta_{1}+\theta_{2})\right}{\cos\theta_{2}}\right)&=350 \\ 
T_{1}&=350 \left(\frac{\cos\theta_{2}}{\sin\left(\theta_{1}+\theta_{2})\right}\right) \\ 
T_{1}&=\frac{350\cos\theta_{2}}{\sin\left(\theta_{1}+\theta_{2})\right} \\
T_{1}&=\frac{350\cos23.8}{\sin\left(55.3+23.8)\right} \\
T_{1}&=\frac{350\cos23.8}{\sin79.1} \\
T_{1}&=\text{326.12 N} \\
\end{align*}

\begin{align*}
T_{1}\sin\theta_{1}&=350 - T_{2}\sin\theta_{2} \\
T_{1}&=\frac{350 - T_{2}\sin\theta_{2}}{\sin\theta_{1}} \\
-\left(\frac{350 - T_{2}\sin\theta_{2}}{\sin\theta_{1}}\right)\cos\theta_{1}+T_{2}\cos\theta_{2}&=0 \\
-\left(\frac{350\cos\theta_{1} - T_{2}\sin\theta_{2}\cos\theta_{1}}{\sin\theta_{1}}\right)+T_{2}\cos\theta_{2}&=0 \\
\frac{-350\cos\theta_{1} + T_{2}\sin\theta_{2}\cos\theta_{1}}{\sin\theta_{1}}+T_{2}\cos\theta_{2}&=0 \\
\frac{-350\cos\theta_{1}}{\sin\theta_{1}} + \frac{T_{2}\sin\theta_{2}\cos\theta_{1}}{\sin\theta_{1}}+T_{2}\cos\theta_{2}&=0 \\
\frac{-350\cos\theta_{1}}{\sin\theta_{1}} + T_{2}\left(\frac{\sin\theta_{2}\cos\theta_{1}}{\sin\theta_{1}}+\cos\theta_{2}\right)&=0 \\
T_{2}\left(\frac{\sin\theta_{2}\cos\theta_{1}}{\sin\theta_{1}}+\cos\theta_{2}\right)&=\frac{350\cos\theta_{1}}{\sin\theta_{1}} \\
T_{2}\left(\frac{\sin\theta_{2}\cos\theta_{1}+\cos\theta_{2}\sin\theta_{1}}{\sin\theta_{1}}\right)&=\frac{350\cos\theta_{1}}{\sin\theta_{1}} \\
T_{2}\left(\frac{\sin\left(\theta_{2}+\theta_{1}\right)}{\sin\theta_{1}}\right)&=\frac{350\cos\theta_{1}}{\sin\theta_{1}} \\
T_{2}&=\frac{350\cos\theta_{1}}{\sin\theta_{1}}\left(\frac{\sin\theta_{1}}{\sin\left(\theta_{2}+\theta_{1}\right)}\right) \\
T_{2}&=\frac{350\cos\theta_{1}}{\sin\left(\theta_{2}+\theta_{1}\right)} \\
T_{2}&=\frac{350\cos55.3}{\sin\left(23.8+55.3)\right} \\
T_{2}&=\text{203 N} \\
\end{align*}
\end{fleqn}
\end{document}

[Frits]

You can use the align command (not align*) and then add \nonumber to all lines that you don't want to number:

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\begin{align*}
T_{2}\cos\theta_{2}&=T_{1}\cos\theta_{1} \label{eq:test}\\ 
T_{2}&=\frac{T_{1}\cos\theta_{1}}{\cos\theta_{2}} \nonumber \\
...
T_{1}&=\text{326.12 N} \nonumber\\
\end{align*}

[ghostanime2001]

LOL that's not what I meant. I should rephrase what I really mean. I want to create a numbered list, except with a block of equations. And only the first line is numbered on the left side AND is INLINE with the number. For example, you know when you do physics problems in school? How you usually start out is on line paper and writing like this:

1. f(x) = 3x+2
.
.
.
T = 346 N

I want it to be like that above^. How can I make this kind of format and still keeping the entire "equation block" left-aligned on the page? (I think I have done this already with \begin{fleqn}...\end{fleqn} environment. But if I were to make the format above. I don't want my left alignment environment removed or changed. Thanks. I hope you know what i mean.

[Juanjo]

Perhaps you are looking for something like this:

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\documentclass[a4paper]{article}
\usepackage[T1]{fontenc}
\usepackage{amsmath}
\begin{document}

Solutions:
\begin{enumerate}
   \item $\begin{aligned}[t]
             \sin^2\alpha+\cos^2\alpha&=1 \\
             1+\tan^2\alpha&=\sec^2\alpha
          \end{aligned}$
   \item $\begin{aligned}[t]
             \sin2\alpha&=2\sin\alpha\cos\alpha \\
             \cos2\alpha&=\cos^2\alpha-\sin^2\alpha
          \end{aligned}$
\end{enumerate}

\end{document}

[ghostanime2001]

hahaha!! my friend, you've made a miracle happen! (it's time to put this to the test) thanksssss!! but i gotta know is this left-aligned to the page margin?

[Juanjo]

but i gotta know is this left-aligned to the page margin?

Load the enumitem package and change \begin{enumerate} by \begin{enumerate}[leftmargin=*]. Read the package manual for more information.

[ghostanime2001]

What does [leftmargin=*] do? Also, Why can't I use fleqn environment?

[svend_tveskaeg]

What does [leftmargin=*] do?

RTFM, as Juanjo has already mentioned! Take a look at p. 3 in the enumitem manual.

[ghostanime2001]

Juanjo

I don't know what you mean.

[ghostanime2001]

How do I make the first equation with the number not indented? What i mean is, how can I line it up with the true left margin of my page?