// Pour les paraboles par 3 points P,Q,R

a1

(x(P)*(y(R)-y(Q))-x(Q)*y(R)+y(Q)*x(R)+y(P)*(x(Q)-x(R)))/(x(P)*(x(R)^2-x(Q)^2)-x(Q)*x(R)^2+x(Q)^2*x(R)+x(P)^2*(x(Q)-x(R)))

b1

-(x(P)^2*(y(R)-y(Q))-x(Q)^2*y(R)+y(Q)*x(R)^2+y(P)*(x(Q)^2-x(R)^2))/(x(P)*(x(R)^2-x(Q)^2)-x(Q)*x(R)^2+x(Q)^2*x(R)+x(P)^2*(x(Q)-x(R)))

c1

(x(P)*(y(Q)*x(R)^2-x(Q)^2*y(R))+x(P)^2*(x(Q)*y(R)-y(Q)*x(R))+y(P)*(x(Q)^2*x(R)-x(Q)*x(R)^2))/(x(P)*(x(R)^2-x(Q)^2)-x(Q)*x(R)^2+x(Q)^2*x(R)+x(P)^2*(x(Q)-x(R)))


xN

-(-sqrt(a1)*sqrt(abs(a))*sqrt(abs(-4*a*c+4*a1*c+4*a*c1-4*a1*c1+b^2-2*b1*b+b1^2))+a*b-a*b1)/(2*a^2-2*a1*a)

xM

-(sqrt(a1)*sqrt(abs(a))*sqrt(abs(-4*a*c+4*a1*c+4*a*c1-4*a1*c1+b^2-2*b1*b+b1^2))+a*b-a*b1)/(2*a^2-2*a1*a)