import math

def quadratic(a,b,c):

    x1=[]

    x2=[]

    #对参数检验

    if not isinstance(a,(int,float)):

        print('bad operand type')

    elif a==0:

        print("a为非零项")

        return None

    if not isinstance(b,(int,float)):

        print('bad operand type')

    if not isinstance(c,(int,float)):

        print('bad operand type')

    #对根判定

    if b**2-4*a*c < 0:

        print("该方程无解")

    else:

        x1 = (-b+math.sqrt(b**2-4*a*c))/(2*a)

        x2 = (-b-math.sqrt(b**2-4*a*c))/(2*a)

        return x1,x2

#实例化

lizi1 = quadratic(2,3,1)

print(lizi1)

lizi2 = quadratic(1,3,-4)

print(lizi2)