为什么是   t = math.sqrt(b * b - 4 * a * c)
题目不是ax*x+bx+c=0吗

def quadratic_equation(a, b, c):

    t = math.sqrt(b * b - 4 * a * c)

    return (-b + t) / (2 * a),( -b - t )/ (2 * a)

求根公式  

#delta = b*b-4*a*c

#d1 = (-b+sqrt(b*b-4*a*c))/(2a)

#d2 = (-b-sqrt(b*b-4*a*c))/(2a)