Do North Koreans use Latin (and Greek) letters in their equations?
On the one hand, being such an isolationist country, I wouldn't be surprised if they used the Korean alphabet (조선글) in their equations. On the other hand, the similarly isolationist Soviet Union used Latin letters in its equations rather than Cyrillic (Кириллица) throughout its history, even in the space and nuclear programs.
Nearby China uses Latin as well (imagine using characters (漢字) as variables! …Actually that would be so cool. But never mind)
Another possibility is that they use the Korean alphabet in elementary education and switch to Latin for more advanced subjects (such as their own rocket and nuclear programs).