I hope Russian is your first language, because that is nearly unreadable in English.

*Snip ramblings as I try various things to figure out what you might mean.*
Well, trying to read through your rough English again, maybe

and

are supposed to be functions, and

,

and

are supposed to be constants. You said

is where the two curves meet, but a line and a parabola will meet in two places. Well, assuming a few things (what's a function and what's a constant and which meeting point), I get the difference between the curves at

to be

.

Also, performing calculations, even complicated ones is not what being a mathematician is about. It's about learning to see and distill paterns (and applied mathematicians find uses for them).