when i change parameters of parabula it make point on the graf undefined
i want check area of triangle witch limited by parabola and axis X. for that i build my triangle by putting one dot on the parabola and 2 on axis x. to make it more flexible i drew parabola by using this formula " ax^2+bx+x " the problem begin if i change parameter a from positive to negative and visa versa. after the change it say the point (C in my program) undefined, until i press the function rectangle in the left area and then the point rectangle there. same happen if i change a value again.
p.s. if i don't limit the parabola between the points it intersect with axis X it don't have such problems
p.s.2 it seem the problem is caused because when putting point on graph the point keeps its axis x position while graph changes