How to write a basic equation in latex (see picture)

Question

How to write these equations in latex?

edit: I want both equations to be in line. So that the equation is in the second equation below.

Answer 1

I’m sorry, but Sebastiano’s is an awful way of using the align* environment. Let's recap a few basic facts:

The source code is:

% My standard header for TeX.SX answers:
\documentclass[a4paper]{article} % To avoid confusion, let us explicitly 
                                 % declare the paper format.

\usepackage[T1]{fontenc}         % Not always necessary, but recommended.
% End of standard header.  What follows pertains to the problem at hand.

\usepackage{amsmath}



\begin{document}

There are several ways to achive such a layout:

\begin{enumerate}
    \item
        Use a plain \texttt{align*} environment:
        \begin{align*}
            (T_{5}g)(t) &= g(t-5) &
                g_{5,\frac12}(t) &= (M_{\frac12}T_{5}g)(t) \\
            &&&= g(t-5)e^{2\pi i\left(\frac12\right)t}
        \end{align*}

        You could also have an equation number on, say, the first line,
        but I~don't think this is what you want:
        \begin{align}
            (T_{5}g)(t) &= g(t-5) &
                g_{5,\frac12}(t) &= (M_{\frac12}T_{5}g)(t) \\
            &&&= g(t-5)e^{2\pi i\left(\frac12\right)t} \notag
        \end{align}

    \item
        A slight variation is to replace \texttt{align*} (resp.,
        \texttt{align}) with \texttt{flalign*} (resp., \texttt{flalign}),
        which aligns the two blocks to the text margins:
        \begin{flalign*}
            (T_{5}g)(t) &= g(t-5) &
                g_{5,\frac12}(t) &= (M_{\frac12}T_{5}g)(t) \\
            &&&= g(t-5)e^{2\pi i\left(\frac12\right)t}
        \end{flalign*}

        Note, however, the awful placement of the equation number:
        \begin{flalign}
            (T_{5}g)(t) &= g(t-5) &
                g_{5,\frac12}(t) &= (M_{\frac12}T_{5}g)(t) \\
            &&&= g(t-5)e^{2\pi i\left(\frac12\right)t} \notag
        \end{flalign}

    \item
        With \texttt{alignat*} (resp., \texttt{alignat}) you are
        responsible for specifying both the number of alignments
        and the horizontal space between them: 
        \begin{alignat*}{2}
            (T_{5}g)(t) &= g(t-5) &\hspace{4em} % = 4*\quad
                g_{5,\frac12}(t) &= (M_{\frac12}T_{5}g)(t) \\
            &&&= g(t-5)e^{2\pi i\left(\frac12\right)t}
        \end{alignat*}

        With equation number(s):
        \begin{alignat}{2}
            (T_{5}g)(t) &= g(t-5) &\hspace{4em} % = 4*\quad
                g_{5,\frac12}(t) &= (M_{\frac12}T_{5}g)(t) \\
            &&&= g(t-5)e^{2\pi i\left(\frac12\right)t} \notag
        \end{alignat}

    \item
        So far we have seen solutions I'd \emph{deprecate};
        let's see now one I'd \emph{recommend}: use an \texttt{alignedat}
        environment.  With this, you can give a unique equation number
        to the whole block of equations, which is probably what you want:
        \begin{equation}
            \begin{alignedat}{2}
                (T_{5}g)(t) &= g(t-5) &\hspace{4em}
                    g_{5,\frac12}(t) &= (M_{\frac12}T_{5}g)(t) \\
                &&&= g(t-5)e^{2\pi i\left(\frac12\right)t}
            \end{alignedat}
        \end{equation}

        Should you later change your mind and decide not to number the
        equation, all you have to do is to add two asterisks
        (to \texttt{equation}, not to \texttt{alignedat}):
        \begin{equation*}
            \begin{alignedat}{2}
                (T_{5}g)(t) &= g(t-5) &\hspace{4em}
                    g_{5,\frac12}(t) &= (M_{\frac12}T_{5}g)(t) \\
                &&&= g(t-5)e^{2\pi i\left(\frac12\right)t}
            \end{alignedat}
        \end{equation*}
\end{enumerate}

\end{document}

Answer 2

If you are primarily looking at writing equations, I like to use KLatexFormula for windows. It allows me to drag and drop a picture of the equation where I want. Here is quick guide I use and found online. A quick guide to latex