MATLAB: How can i find angle with x-axis of a plot in matlab

angleslope

my plot curve is y = p1*x^2 + p2*x + p3

Coefficients:

p1 = 0.00053537

p2 = -8.1393e-018

p3 = -0.00044699

i want to find each point's angle with x axis . . .

p1 = 0.00053537
p2 = -8.1393e-018
p3 = -0.00044699
x=0:0.1:10
y = p1*x.^2 + p2*x + p3
angles=angle(x+j*y)

for P1 = 0 : .1 : 1
  for P2 = 0 : .1 : 1-P1
    P3 = 1 - P1 - P2;
      .... do whatever ...
  end
end

z = a*x+b*x^2+c+........; 
eqn = subs(sym('D2y +5*z+ 2*x + 10*z^2'), z, z);
S = dsolve(eqn, x);

Myself, I would probably toss in a simplify() around the subs() .