im trying to write a code that i can input a,b,c and the code will run it in the quadratic formula and give me the answer but i keep getting a error problem

import math

from math import sqrt

print

print ("Welcome to the Quadratic Program")

print ("--------------------------------")

print

a=input("Enter a: ")

b=input("Enter b: ")

c=input("Enter c: ")

print

print

answer=[b+(math.sqrt((b*b)-(4*a*c)))]/(2*a)

if answer<0:

print ("negative")

print answer