import math 

def quadratic(a,b,c):
    x = b*b-4*a*c
    if  x > 0:
        y = ((-b + math.sqrt(x))/(2*a),(-b - math.sqrt(x))/(2*a))
        return print('x1=%.2f,x2=%.2f' % (list(y)[0],list(y)[1]))
    elif x == 0:
        return print('x1=x2=%.2f' % math.sqrt(x)/(2*a))
    else:
        return print('方程无实根！')

quadratic(1,6,7)