课时作业21
Ⅰ.阅读理解
(2017·河南省鹤壁市高级中学周练)
Edmund Halley was an English scientist who lived over 200 years ago. He studied the observations of comets (彗星) which other scientists had made. The orbit(轨道)of one particular comet was a very difficult mathematical problem. He could not figure it out. Neither could other scientists who dealt with such problems.
However, Halley had a friend named Isaac Newton, who was a brilliant mathematician. Newton thought he had already worked out that problem, but he
