请写出勾股定理：“直角三角形的两直角边的平方和等于斜边的平方”的逆定理： ．
如果一个三角形的两边平方和等于第三边平方，那么这个三角形为直角三角形
题目分析：先把命题分成题设和结论两部分，然后让结论当题设，题设当结论即可．
原命题可变为：如果一个三角形是直角三角形，那么它的两直角边的平方和等于斜边的平方．
我们把题设和结论变换位置即可：如果一个三角形的两边的平方和等于第三边的平方，那么这个三角形为直角三角形．
点评：本题属于基础应用题，只需学生熟练掌握原命题与逆命题的关系，即可完成．
Bobby walked on the sidewalk. He walked past the park. He saw the kids playing. "Why don't they want to play with me ?” he thought.
It was a mystery（谜）to him. Oh , sure. He was new in town . They moved to the town just two months ago. He knew it was hard to make new friends . 小题1:
At the same time , Cassie watched Bobby from the park. Every day she saw this boy walk by slowly .
小题2: " Why doesn't he want to play with us?" she thought. Oh, sure. He was new in town. But she'd tried to say "Hi" to him. It was a mystery to her.
The days went on. Bobby walked to and from school alone. He always felt bad about not having friends. Cassie kept saying" Hi" but they never talked more.小题3:
Bobby kept thinking about it.小题4: Finally , three weeks before the end of school , Cassie had an idea. "I'm not sure why he doesn't seem to want friends.小题5:. I'm going to invite him to my birthday party. " Cassie wrote an invitation to invite Bobby to her birthday party.
"Will Bobby come to my birthday party?" she was not sure, It was still a mystery to her.
| A. He never stopped. B. He is so crazy. C. But I am going to try harder. D. But he still didn't understand. E. Cassie kept thinking about it. F. I'm not interested in playing it. G. What was the problem? |