b = 2.1e4;
c=  1.e0;

x1 = ( -b+sqrt(b^2-4*c) )/2
x2 = ( -b-sqrt(b^2-4*c) )/2
x1p = c/x2

(x1-x1p)/x1p

bb = vpa(2.1e4,32);
cc = vpa(1.e-0,32);
xx1 = (-bb + sqrt( bb^2-4*cc ) )/2
xx2 = (-bb - sqrt( bb^2-4*cc ) )/2
xx1p = c/xx2