It was supposed to a High school level math, so she thought she could solve it and brought it, but as you'd expect from your average adult she remembers doing that kinda math in school but forgot how to actually solve it.... And was cursing herself for not paying enough attention to class, then the prince solves it later.
It wasn't supposed to be a formula in ancient language
https://thewebnovelhaven.wordpress.com/the-heroine-had-an-affair-with-my-fiance/
here you go but only the main story is complete though
I thought that was a different purple haired “villainess”. Sounds like “Isn’t being a wicked woman much better”. Was this novel about math too? Maybe they changed it because “Isn’t being a wicked woman much better, because two purple haired villainess who solve magic formulas via high school math might be a but much
why the hell they changed a lot of the original plot from the novel in the manhwa???