incorrect answers for quadratic equations

Question

I was wondering if anyone could tell me why my python code for solving quadratic equations isn't working. I have looked through it and haven't found any errors.

print("This program will solve quadratic equations for you")

print("It uses the system 'ax**2 + bx + c'")

print("a, b and c are all numbers with or without decimal \
points")

print("Firstly, what is the value of a?")

a = float(input("\n\nType in the coefficient of x squared"))

b = float(input("\n\nNow for b. Type in the coefficient of x"))

c = float(input("\n\nGreat. now what is the c value? The number alone?"))

print("The first value for x is " ,(-b+(((b**2)-(4*a* c))* * 0.5)/(2*a)))

print("\n\nThe second value for x is " ,(-b-(((b * * 2)-(4*a*c))** 0.5)/(2*a)))

When a=1 b=-4 and c=-3 I am expecting -1 and 4 but get 5.5 and 0.5

Answer 1

Your trouble is in the part that tries to do the quadratic formula:

(-b+(((b**2)-(4*a* c))* * 0.5)/2*a)

The trouble is that * has the same precedence as / so you're dividing by 2 and then multiplying by a. Also your parentheses are off, so I reduced the unnecessary ones and moved the wrong ones. In short, -b wasn't being put together with the square root before the division. What you want is:

(-b+(b**2-4*a*c)**0.5)/(2*a)

P.S. For the sake of asking questions, it would be better to ask in the form of something like:

>>> a = 2
>>> b = 1
>>> c = 3
>>> (-b+(((b**2)-(4*a* c))* * 0.5)/2*a)
got blah, expected blam

Since the other printing and inputting is not to blame (which you should be able to work out fairly easily).