2 of 4 added 61 characters in body

## Python 3, 79 chars

a,b,c=eval(input())
d=(b*b-4*a*c)**.5/2/a
x=-b/2/a
print('r1=',x+d,'\nr2=',x-d)


Python's imaginary unity is j and not i. I used Python 3 because the power operator works also on negative numbers.

BTW, is it really needed to write r1= ... and r2= ... ?