Ah thanks, I know Symbolic, but I can't use it in programs (no idea why).
At first the good message: I've programmed such an application yesterday and it's almost finished.
The bad message: It does only work with Quadratic functions like -2x² + 6x + 8 or (x + 2)² - 3 (no sin(x), cos(x), tan(x), ...).
By the way, is there a way to find the zeros of a function in Y1 without using the solve() command?
// Edit: I made some screenshots. That is what i got so far.