def TTC(x1,y1,x2,y2,v1x,v1y,v2x,v2y,l):

    a = pow(v1x-v2x,2) + pow(v1y-v2y,2)
    b = 2 * ((x1-x2) * (v1x-v2x) + (y1-y2) * (v1y-v2y))
    c = pow(x1-x2,2) + pow(y1-y2,2) - pow(l,2)
    
    if pow(b,2) >= 4*a*c:
        ttc1 = (-b + sqrt(pow(b,2) - 4*a*c)) / (2*a)
        ttc2 = (-b - sqrt(pow(b,2) - 4*a*c)) / (2*a)
        if ttc1 >= 0 and ttc2 >= 0:
            ttc = min(ttc1,ttc2)
        else:
            if ttc1 < 0:
                ttc = ttc
            if ttc2 < 0:
                ttc = ttc1
            if ttc1 < 0 and ttc2 < 0:
                ttc = []
    else:
        ttc = []

    return ttc