问题
填空题
已知α、β表示两个不同的平面，m为平面α内的一条直线，则“α⊥β”是“m⊥β”的______条件．
答案
由平面与平面垂直的判定定理知，m为平面α内的一条直线，如果m⊥β，则α⊥β；
反过来m为平面α内的一条直线，则“α⊥β”可能有m∥β，m∩β=p，可能有m⊥β三种情况．
所以“α⊥β”是“m⊥β”的必要不充分条件．
故答案为：必要不充分
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已知α、β表示两个不同的平面，m为平面α内的一条直线，则“α⊥β”是“m⊥β”的______条件．
由平面与平面垂直的判定定理知，m为平面α内的一条直线，如果m⊥β，则α⊥β；
反过来m为平面α内的一条直线，则“α⊥β”可能有m∥β，m∩β=p，可能有m⊥β三种情况．
所以“α⊥β”是“m⊥β”的必要不充分条件．
故答案为：必要不充分
| 阅读理解。 | |
protection. Mr Zhao, 1________, told us that he was very worried about the pollution in our city. He said that our city used to be a beautiful one with a very wonderful natural landscape, such as green mountains, clean water, fresh air and so on. But now, 2________. Have you ever littered? Have you ever spat (吐痰) in a public place? Have you ever drawn casually on walls? If your answers are "Yes", 3________ . You can also ask yourself: "Have I ever picked up dirty paper and thrown it into a dustbin? Have I ever collected bottles for recycling? Have I ever planted trees or flowers?" If your answers are still "Yes", that shows you've made a contribution to the environmental protection. I think 4 ________, but also the problem of all the cities in our country and even in the world. And it's not only the duty of the people in our city, but also of all the people on the earth to protect the environment, 5 ________. Do it from now on. Do it from every small thing around us. Then we will have a more beautiful and cleaner earth. |