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How would I go about adding a subscript to a symbol I'm defining from an equation. For example I have an equation

E_m = \alpha_m x + y

How can I then do something like \emph \alpha\textsubscript{m}

The above gives me errors and I can't figure out how to correct this.

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why don't you just set the substring as math? i.e., $\alpha_m$ -- \emph usually sets its argument in italic, and that's the usual math style. – barbara beeton May 2 '12 at 15:45
Such a formula should be typed as \(E_{m}=\alpha_{m}x+y\): TeX will take care of the details of math mode. – egreg May 2 '12 at 15:45
Welcome to TeX.SE. Do you want the subscript in italic, or roman? The usual $E_{m} = \alpha_{m} x + y$ will give you italics, and $E_m = \alpha_{\mathrm{m}} x + y$ will give you a roman subscript. – Peter Grill May 2 '12 at 16:44
That's brilliant, thank you for your help. – oxidising May 2 '12 at 17:04

Math formulas should be written in "math mode":


is the correct way to input that formula.

The "Not so short introduction to LaTeX" covers this topic and is available in many languages.

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