Russian mathematical notation or peculiarities of Russian notation in mathematics:
$English \;-\;Russian$
$3.14 \;-\;3,14\;\;$(in Russian, dots are not used for decimal fractions)
$1,000,000\;-\;1.000.000$
$\$100\;-\;100\$$
Point $A(1,2) \;-\; A(1;2)$
$tan\,x \;-\;tg\,x$
$cot\,x \;-\;ctg\,x$
$sinh\,x \;-\;sh\,x$
$cosh\,x \;-\;ch\,x$
$tanh\,x \;-\;th\,x$
$coth\,x \;-\;cth\,x$
$sin^{-1}\,x\;-\;arcsin\,x\;$ (and so on for other inverse trig functions but the general sign for inverse functions is exactly the same e.g., $f^{-1}.\;$Note that we also use $arcsin$ etc. in some UK/US books like those by Serge Lang. It's also used in other languages and universally understood). Yet something like $arch\,x$ may look arcane but it is not if you look a few lines above.
${{n}\choose{k}}\;-\; C_n^k\;\;$ (it is backwards!)
$P_{n,k}\;-\; A_n^k\;\;$ (backwards again)
(And $\;m!\;$ as permutations is the same in Russian: $P_m$)
In elementary algebra (not complex variables):
$log\,x\;-\;lg\,x\;\;$(common or decimal logarithm with base $10$)
In geometry everything seems to be the same (all symbols, denotations etc.) but area is never denoted by the letter A, it's denoted with the English letter S. Volume, however is similarly denoted by V.
Long division looks weard--google the Russian words 'деление столбиком' and see all the pictures! Also, note that letters A, B..., a,b,c... are pronounced like in Latin!
Although it looks like there is some significant difference in notation, it's not the case. Almost everything in all math branches looks exactly the same when compared with Russian texts. So much so that it is difficult for me to come up with some other differences. I can, at a push, say things like: In Russian books parabola is always $y^2=2px$ instead of $y^2=4px$ but you can come up with various subtleties from book to book. Simply put, notation may slightly differ in various Russian books as it may also differ in some English books. And there are even fewer differences in notation when it comes to higher branches of mathematics.