I am having some difficulties in understanding what my graph is showing me in MATLAB.

I have chosen the value for a,b and c for the quadratic so the result will be complex, however the graph does not point to the values when the function cross the 0 axis. the first one does but according to the results the second should be in the third quadrant.

a = 1;

b = 0.009;

c = 5;

x =linspace(-16,16);

y = a*x .* x + b*x + c

plot(x,y)

x1=(-b+sqrt((b^2)-(4*a*c)))/(2*a)

x2=(-b-sqrt((b^2-4)*(a*c)))/(2*a)

The two roots are as follows:

x1 = -0.0045 + 2.2361i

x2 = -0.0045 - 2.2360i

x1= seems to be correct, however x2 is somewhere in the third quadrant this is not reflected on the graph generated by MATLAB.

I know this is something I am doing wrong I would appreciate it, if someone will show me the error of my ways.