题目

We all want our skin (皮肤) to look good. If our skin is clear and healthy, it makes you feel better about yourself. How do you get great skin? Here are some suggestions.Protect your skin against the sun.If you are going to be outside, especially in the sun, you should put on sun cream (防晒霜) in summer.Wear a hat to protect your face. A wide hat is the best, as it will protect your ears and neck as well.Stay in the shade whenever you can.Use sun cream about half an hour before going outside.How to wash your skin?Wash your body all over once a day. Use mild soap (肥皂) and warm water t已知线段AB过轴上一点，斜率为，两端点A，B到轴距离之差为，（1）求以O为顶点，轴为对称轴，且过A，B两点的抛物线方程；（2）设Q为抛物线准线上任意一点，过Q作抛物线的两条切线，切点分别为M，N，求证：直线MN过一定点；