LaTeX uses italics in math mode for variables to make them stand out, but Roman (non-italic) for function names. How is LaTeX to know the difference between ``sin'' as function name and ``sin'' as the product of the variables s, i, and n? Use a backslash in front of ``sin'' and other function names to let LaTeX know that you want the function, not the product of variables.
Here is a list of function names:
\arccos |
\arcsin |
\arctan |
\arg |
\cos |
\cosh |
\cot |
\coth |
\csc |
\deg |
\det |
\dim |
\exp |
\gcd |
\hom |
\inf |
\ker |
\lg |
\lim |
\liminf |
\limsup |
\ln |
\log |
\max |
\min |
\Pr |
\sec |
\sin |
\sinh |
\sup |
\tan |
\tanh |