>>  a = -73.4

a = -73.400

>>  b = 6.0

b =  6

>>  c = 13.1

c =  13.100

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

x = -0.38356

>>  check = a*x^2 + b*x + c

check = -1.7764e-15