题目

在平面直角坐标系O中，直线与抛物线相交于、 两点。 （Ⅰ）求证：“如果直线过点，那么＝”是真命题； （Ⅱ）写出（Ⅰ）中命题的逆命题，判断它是真命题还是假命题，并说明理由。 答案：（Ⅰ）证明见解析。 （Ⅱ）（Ⅰ）中命题的逆命题：在平面直角坐标系O中，直线与抛物线＝2相交于、两点。如果 ＝，那么直线必过点。它是假命题，理由见解析。 解析:（Ⅰ）证明：如果直线轴，则；如果直线与轴不垂直，设直线的方程为，    。综上，“如果直线过点，那么＝”是真命题。 （Ⅱ交际练习 　　在所给选项中挑出最佳答案完成所给对话： 　　Leta：What's your opinion about nuclear energy（核能）？ 　　Bill： Well, 1 , nuclear energy is our best hope for the future . 　　Leta： But don't you think it' s dangerous to the people living near the nuclear power plants (核电厂) ? 　　Bill： Not really. 2 , nuclear energy is a clean and safe source (资源) of electricity . 　　Leta： Well, 3 , people don't realize how dangerous the radiation (射线) can be. 　　Bill： The thing to keep in mind is that our coal, oil and gas resources are limited. 　　 Leta： Let me say one more thing. 4 . 　　Bill： You know, we could probably (或许) go on talking about this for ever (永远). 　　Leta： You are probably right. 5 when it comes to nuclear energy . 　　Bill ： I agree with you on that. (1) [　　] A．everyone' s willB．in your opinion C．my opinionD．in my opinion (2) [　　] A．UnfortunatelyB．So far as I know C．First of allD．I am sorry . (3) [　　] A．if you don't ask meB．as I see it C．as I can't seeD．until I ask you (4) [　　] A．I don't think any accidents can happen at nuclear power plants in the world B．there is no doubt that no accidents have ever happened when we make use of nuclear energy C．many accidents happened at nuclear power plants in several countries D．it doesn't seem that any accidents about nuclear power plants have once happened (5) [　　] A．I guess we'll never agree with each other B．I feel we won't disagree with each other C．I believe we'll agree with each other D．I don't suppose we'll disagree with each other