Python二次公式无效

Question

我正在尝试创建一个简单的程序，以便为python中的二次方程的根提供唯一答案，但我的代码不起作用。以下是我到目前为止所拥有的：

from math import *
def qf(a, b, c):
    print((-b+sqrt(b*b-4*a*c))/(2*a));
    print((-b-sqrt(b*b-4*a*c))/(2*a));
while(True):
    qf(input("A: "), input("B: "), input("C: "))

以下是我在评估时遇到的错误：

Traceback (most recent call last):
  File "qf.py", line 6, in <module>
    qf(input("A: "), input("B: "), input("C: "))
  File "qf.py", line 3, in qf
    print((-b+sqrt(b*b-4*a*c))/(2*a));
ValueError: math domain error

我犯了什么错误，怎么改正呢？

Answer 1

试试这个：

from math import *
def qf(a, b, c):
    if b*b < 4*a*c:
        print("cannot compute qf({}, {}, {})".format(a, b, c))
        return
    print((-b+sqrt(b*b-4*a*c))/(2*a));
    print((-b-sqrt(b*b-4*a*c))/(2*a));
while(True):
    qf(float(input("A: ")), float(input("B: ")), float(input("C: ")))

您需要确保不将负值传递给sqrt()。此外，您应该将input()的结果转换为数字类型。

Answer 2

此代码允许您在四分式等式中输入三个值，并返回根或没有根的状态：

import math
def solveQuadratic(a,b,c):
    dis = discriminant(a,b,c)
    if dis < 0:
        print('no real roots')
    else:
        sqdis = math.sqrt(dis)
        topOne = -b+sqdis
        B = 2*a
        firstRoot = topOne/B
        firstRoot = str(firstRoot)
        print ('the first root is: '+firstRoot)
        topTwo = -b-sqdis
        B = 2*a
        secondRoot = topTwo/B
        secondRoot = str(secondRoot)
        print ('the second root is: '+secondRoot)
def discriminant(a,b,c):
    fp = b*b
    ac = a*c
    sp = -4*ac
    dis = fp+sp
    return (dis)

print('enter first coefficient')
a = input()
a = int(a)
print('enter second coefficient')
b = input()
b = int(b)
print('enter the constant')
c = input()
c = int(c)
solveQuadratic(a,b,c)