My guess is that is not an x, but more likely a \kappa, similar to https://commons.wikimedia.org/wiki/File:Greek_lowercase_kappa_variant.svg
– Steven B. SegletesDec 01 '20 at 15:31
Note that the kappa symbol is slanted after d, but it is unslanted after sin, cos. It seems that your picture is a result of typesetting work of an amateur. The integral symbol is from bold variant of a math font but the rest isn't.
– wipetDec 01 '20 at 15:46
@RobertW. My tip is that this is not TeX (i.e. no LaTeX, no latex package). There are slanted/unslanted version of kappa, the spaces between sin, cos and their arguments are missing, there is a mix of bond/nobold symbols. Of course, I am able to do such obscure things by TeX, but it is more complicated task:).
– wipetDec 01 '20 at 15:57
1 Answers1
7
I think this is the symbol \varkappa (you need the package amssymb).
x, but more likely a\kappa, similar to https://commons.wikimedia.org/wiki/File:Greek_lowercase_kappa_variant.svg – Steven B. Segletes Dec 01 '20 at 15:31