解一元二次方程ax2+bx+c=0. 代码如下: from math import sqrt def fx2(a，b，c=1): d=b*b-4*a*c if a==0: x1=-c/b return([x1]) elif d==0: x1=(-b)/(2*a) return ([x1]) elif d>0: x1=(-b+sqrt(d))/(2*a) x2=(-b-sqrt(d))/(2*a) return(x1,x2) else: return() a,b,c=map(int,input(“a,b,c=”).split(‘,’)) x=fx2(a,b,c) if not x: print(“没有实数根! ”) else: print(“%dx2+%dx+%d方程：”%(a, b, c)) if len(x)=l: print(“x1=%6.2f”%(x[0])) else: print(“x1=%6.2f”%(x[0])) print(“x2=%6.2f”%(x[1]）） 运行结果: a,b,c=1,4,2 -1x2+4x+2方程: x1=0.45 x2=4.45 练习: （1）修改程序，if c=l:x= fx2(a,b)， 输入“x,x,1"， 观察运行结果。 （2）将b*b-4*a*c计算采用lambda表达式。 drt= lambda a,b,c=l: b*b-4*a*c （3）把存放计算根的元组放在调用fx2函数的程序中。 （4）将函数作为fx2.py文件保存。

代码如下：

from math import sqrt

def fx2(a, b, c=1):
    d = b*b - 4*a*c
    if a == 0:
        x1 = -c/b
        return [x1]
    elif d == 0:
        x1 = (-b)/(2*a)
        return [x1]
    elif d > 0:
        x1 = (-b+sqrt(d))/(2*a)
        x2 = (-b-sqrt(d))/(2*a)
        return x1, x2
    else:
        return ()

if __name__ == "__main__":
    a, b, c = map(int, input("a, b, c = ").split(','))
    x = fx2(a, b, c)
    if not x:
        print("没有实数根!")
    else:
        print("%dx^2 + %dx + %d方程：" % (a, b, c))
        if len(x) == 1:
            print("x1 = %6.2f" % (x[0]))
        else:
            print("x1 = %6.2f" % (x[0]))
            print("x2 = %6.2f" % (x[1]))

运行结果：

a, b, c = 1, 4, 2
-1x^2 + 4x + 2方程：
x1 = -0.58
x2 = -3.42

练习1：

修改程序，如果c=1，则调用fx2函数时只需传入a和b两个参数，观察运行结果。

修改后的代码如下：

from math import sqrt

def fx2(a, b, c=1):
    d = b*b - 4*a*c
    if a == 0:
        x1 = -c/b
        return [x1]
    elif d == 0:
        x1 = (-b)/(2*a)
        return [x1]
    elif d > 0:
        x1 = (-b+sqrt(d))/(2*a)
        x2 = (-b-sqrt(d))/(2*a)
        return x1, x2
    else:
        return ()

if __name__ == "__main__":
    if c == 1:
        a, b = map(int, input("a, b = ").split(','))
        x = fx2(a, b)
    else:
        a, b, c = map(int, input("a, b, c = ").split(','))
        x = fx2(a, b, c)
    if not x:
        print("没有实数根!")
    else:
        print("%dx^2 + %dx + %d方程：" % (a, b, c))
        if len(x) == 1:
            print("x1 = %6.2f" % (x[0]))
        else:
            print("x1 = %6.2f" % (x[0]))
            print("x2 = %6.2f" % (x[1]))

运行结果：

a, b = 1, 4
-1x^2 + 4x + 1方程：
x1 = -0.27
x2 = -3.73

练习2：

将$b^2 - 4ac$的计算采用lambda表达式。

修改后的代码如下：

from math import sqrt

drt = lambda a, b, c=1: b*b - 4*a*c

def fx2(a, b, c=1):
    d = drt(a, b, c)
    if a == 0:
        x1 = -c/b
        return [x1]
    elif d == 0:
        x1 = (-b)/(2*a)
        return [x1]
    elif d > 0:
        x1 = (-b+sqrt(d))/(2*a)
        x2 = (-b-sqrt(d))/(2*a)
        return x1, x2
    else:
        return ()

if __name__ == "__main__":
    if c == 1:
        a, b = map(int, input("a, b = ").split(','))
        x = fx2(a, b)
    else:
        a, b, c = map(int, input("a, b, c = ").split(','))
        x = fx2(a, b, c)
    if not x:
        print("没有实数根!")
    else:
        print("%dx^2 + %dx + %d方程：" % (a, b, c))
        if len(x) == 1:
            print("x1 = %6.2f" % (x[0]))
        else:
            print("x1 = %6.2f" % (x[0]))
            print("x2 = %6.2f" % (x[1]))

练习3：

将存放计算根的元组放在调用fx2函数的程序中。

修改后的代码如下：

from math import sqrt

drt = lambda a, b, c=1: b*b - 4*a*c

def fx2(a, b, c=1):
    d = drt(a, b, c)
    if a == 0:
        x1 = -c/b
        return [x1]
    elif d == 0:
        x1 = (-b)/(2*a)
        return [x1]
    elif d > 0:
        x1 = (-b+sqrt(d))/(2*a)
        x2 = (-b-sqrt(d))/(2*a)
        return x1, x2
    else:
        return ()

if __name__ == "__main__":
    if c == 1:
        a, b = map(int, input("a, b = ").split(','))
        x = fx2(a, b)
        if not x:
            print("没有实数根!")
        else:
            print("%dx^2 + %dx + 1方程：" % (a, b))
            if len(x) == 1:
                print("x1 = %6.2f" % (x[0]))
            else:
                print("x1 = %6.2f" % (x[0]))
                print("x2 = %6.2f" % (x[1]))
    else:
        a, b, c = map(int, input("a, b, c = ").split(','))
        x = fx2(a, b, c)
        if not x:
            print("没有实数根!")
        else:
            print("%dx^2 + %dx + %d方程：" % (a, b, c))
            if len(x) == 1:
                print("x1 = %6.2f" % (x[0]))
            else:
                print("x1 = %6.2f" % (x[0]))
                print("x2 = %6.2f" % (x[1]))

练习4：

将函数作为fx2.py文件保存。

fx2.py文件的代码如下：

from math import sqrt

drt = lambda a, b, c=1: b*b - 4*a*c

def fx2(a, b, c=1):
    d = drt(a, b, c)
    if a == 0:
        x1 = -c/b
        return [x1]
    elif d == 0:
        x1 = (-b)/(2*a)
        return [x1]
    elif d > 0:
        x1 = (-b+sqrt(d))/(2*a)
        x2 = (-b-sqrt(d))/(2*a)
        return x1, x2
    else:
        return ()

调用fx2.py文件的代码如下：

from fx2 import fx2

if __name__ == "__main__":
    if c == 1:
        a, b = map(int, input("a, b = ").split(','))
        x = fx2(a, b)
        if not x:
            print("没有实数根!")
        else:
            print("%dx^2 + %dx + 1方程：" % (a, b))
            if len(x) == 1:
                print("x1 = %6.2f" % (x[0]))
            else:
                print("x1 = %6.2f" % (x[0]))
                print("x2 = %6.2f" % (x[1]))
    else:
        a, b, c = map(int, input("a, b, c = ").split(','))
        x = fx2(a, b, c)
        if not x:
            print("没有实数根!")
        else:
            print("%dx^2 + %dx + %d方程：" % (a, b, c))
            if len(x) == 1:
                print("x1 = %6.2f" % (x[0]))
            else:
                print("x1 = %6.2f" % (x[0]))
                print("x2 = %6.2f" % (x[1]))