Control point C is the middle point of P2
and P3. Point M is the middle point of P1
Since Start point P1, end point P2, and coordinates
X of control C are free points,
formulas are not necessary.
Coordinate Y of point C is apparently the
value that is subtracted
length of NC from coordinate Y of point
as above figure shows.
For coordinates of points P2 and P3, please click here.