# Correct format of an equation

I have this equation:

$$B_{1} = 0.9(B_{2}) + \\ \bigg[ \sqrt{(x_{1}^2 + y_{1}^2 + z_{1}^2)}-\sqrt{(x_{2}^2 + y_{2}^2 + z_{2}^2)} \bigg]$$


I heard the B_{1} is some kind of result (like a sum, product, etc.) and must be declared as such, so TeX applies the math style guide - correct appearance on it.

But I dont know what it is and how to mark it. Which command can I use here?

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Do you mean summation? – Harish Kumar Mar 24 '12 at 8:44

You can't have a line break in an equation environment, so the \\ does nothing.

A better way to type the equation could be

$$B_{1} = 0.9\,B_{2} + \Bigl[ \sqrt{(x_{1}^2 + y_{1}^2 + z_{1}^2)}- \sqrt{(x_{2}^2 + y_{2}^2 + z_{2}^2)} \; \Bigr]$$


so that the various components of the equation are more visible.

I've made a couple of changes:

• \Bigl[ for the opening bracket and \Bigr] for the closing one (as \bigg size seems too much). Notice the final l or r to declare the type of delimiter;

• a thin space \, between the decimal number 0.9 and B_{2} (which I wouldn't put in parentheses), as the result of 0.9B_{2} might be confusing;

• a thick space between the second square root and the closing bracket for symmetry with the space at the start.

There is no special way to mark B_{1}: it's just a symbol with a subscript.

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this is very helpful, but my prof really told me the B_{1} can´t be italic because it´s something different like the "x" which would be correct as italic. I mean it must be something like a special type of result that mathematicans wouldnt write italic. – dan Mar 24 '12 at 8:57
I don't really know: you should look in the literature in your field in order to see what's the usual form. Maybe \mathrm{B}_{1}? – egreg Mar 24 '12 at 9:05
or \mathbf{B}_{1}? – Harish Kumar Mar 24 '12 at 9:12
I will use that, thank you! I was hoping someone could tell me how you would call the "B", but I guess I should go to maths.stackexchange for that. Thank you guys! – dan Mar 24 '12 at 9:14
@dan With french notations, we need to use \usepackage[upright]{fourier}. I think some other packages for fonts have this option (upright) – Alain Matthes Mar 24 '12 at 9:14