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= ... ?