二次方程的错误答案

Question

我想知道是否有人能告诉我为什么我的解决二次方程的python代码不起作用.我已经浏览过它并且没有发现任何错误.

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)))

当a = 1 b = -4且c = -3时,我期待-1和4但得到5.5和0.5

Answer 1

你的麻烦在试图做二次公式的部分:

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

问题在于它*具有相同的优先级,/因此您将除以2然后乘以a.你的括号也是关闭的,所以我减少了不必要的,并移动了错误的.简而言之,-b在分裂之前没有与平方根放在一起.你想要的是:

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

PS为了提问,最好以下列形式询问:

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

由于其他打印和输入不是责任(你应该能够很容易地解决).