format long % show all the digits

a = 1; b = -(1e6+1e-6); c = 1;

First, we find the "good'' root using the quadratic forumla.

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

Then we use the better formula for computing the other root.

x2 = c/(a*x1)