题干

阅读下面材料:在数学课上,老师给同学们布置了一道尺规作图题:

尺规作图:作Rt△ABC,使其斜边AB=c,一条直角边BC=a.已知:如图1,正比例函数和反比例函数的

图象分别交于M、N两点.

要求:在y轴上求作点P,使得∠MPN为直角.

小丽的作法如下:如图2,以点O为圆心,以OM长为半径作⊙O,

⊙O与y轴交于P1、P2两点,则点P1、P2即为所求.

老师说:“小丽的作法正确.”

请回答:小丽这样作图的依据是____

上一题 下一题 0.0难度 选择题 更新时间:2018-04-21 09:23:34

答案(点此获取答案解析)

半圆(或直径)所对的圆周角是直角

同类题3

阅读理解

    We often hear stories of animals rescuing people .But now someone has managed to return the favor .

    The event took place one snowy January morning Thomas Smith was walking his dog, Jack, in the park." As I was walking, I just saw Jack running onto the ice towards the ducks in the middle, and then he fell into the water and couldn't climb out, "said Smith.  He realized he had no choice but to try and save his dog." someone else told me the lake was only one - meter deep, but it was at least twice that. I had to break my way through the 6- cm ice. Finally, I got Jack by the neck, and pulled him out. I don't think I have ever felt so cold by the time we got back to dry land. And when we got there, everyone was asking if Jack was okay------ no one was particularly worried, about me!"

    A neighbor, Julie Brown, saw it all happen."The dog went onto an icy lake. All of a sudden, it started to go under. There were crowds of people around, and they were all shouting and screaming. Before I knew it, the owner Smith was in the water forcing his way through the ice. I can't begin to imagine how cold it was. Everyone was very nervous, but he was as cool as a cucumber — he just crawled back out, put the dog on its lead, and went home."

    Many regard him as a hero, but Mr. Smith is quite laid- back about it."Most dog owners are the same as me.They would do what I did without a second thought. But in the future, I'm going to make sure he's on lead near any ice ponds,

    Pets are members of our family. Would you do the same for them?