partial solution to exercise 2.5 of http://ocw.mit.edu/courses/electrical-engineering-and-computer-science/6-189-a-gentle-introduction-to-programming-using-python-january-iap-2011/assignments/MIT6_189IAP11_hw2.pdf

homework_2.5.py

# ********** Exercise 2.5 **********

# code for roots function
# given the coefficients for a quadratic equation
# returns the two roots
# if the roots are complex, exit
def find_roots(a,b,c):
    # give up if the roots are complex
    assert not roots_are_complex(a,b,c)
    d = math.sqrt(b**2 - 4*a*c)
    root1 = (-1*b + d)/2*a
    root2 = (-1*b - d)/2*a
    return root1, root2

# given the coefficients for a quadratic equation
# returns true if the roots are complex
# THIS DOESN'T ACTUALLY WORK
def roots_are_complex(a,b,c):
    return False

# Test Cases
print "roots of x^2 + 2x + 1 are ", find_roots(1,2,1)
print "roots of x^2 + 4x + 1 are ", find_roots(1,4,1)
print "roots of x^2 + 4x are ", find_roots(1,4,0)
print "roots of 16x^2 + 4x + 16", find_roots(16,4,16)