题目

     We can often see some automats(自动售货机) everywhere in big cities. It will sell us products by itself. During the progress, there are no shop assistants(助手). So we call the machine—automat.      These days, a new kind of automat was invented. It uses facial recognition(面部识别) technology to refuse some customers. Which customers will be refused? It will refuse some customers who shouldn’t have snacks or drinks. How does it work? First, there is a little Touch TV on the automat. But mostly, it looks like a common automat. It can be programmed(编程) to 二次函数y=x2+4x+6的最小值为        .