Is vector watching to dot(0, 0, 0)

function isVectorWatchingMe(startPoint, endPoint, error)
    function isInSphere(pointArr, radius)
        return math.sqrt(pointArr[1]^2+pointArr[2]^2+pointArr[3]^2) <= radius
    end
    function len(point1, point2)
        return math.sqrt((point1[1]-point2[1])^2+(point1[2]-point2[2])^2+(point1[3]-point2[3])^2)
    end
    function threshold(from, to, value)
        if value <= to or value >= from then
            return true
        end
        return false
    end
    local ang = {
        {
            math.atan2(startPoint[1], startPoint[2]),
            math.atan2(startPoint[3], startPoint[2])
        },
        {
            math.atan2(endPoint[1], endPoint[2]),
            math.atan2(endPoint[3], endPoint[2])
        }
    }
    if error == 0 or error == nil then
        return ang[1][1] == ang[2][1] and ang[1][2] == ang[2][2]
    else
        return math.sqrt((ang[1][1] - ang[2][1])^2 + (ang[1][2] - ang[2][2])^2) <= error^2
    end
    return false
end
-- next code you do not need, this is just for test.
info = {
{0, 0, 0},
{4, 4, 4},
{3, 3, 3}
}
print(isVectorWatchingMe(info[2], info[3], 0.1))