题目

相交弦定理、割线定理、切割线定理在表述形式上非常类似，定理中都涉及到两条线段的积相等，那么这些定理有什么内在联系？定理中两条线段的积能确定具体数值吗？ 答案：思路:相交弦定理、割线定理、切割线定理和切线长定理统称为圆幂定理，圆幂定理是圆和相似三角形结合的产物.每条线段的两个端点一个是公共点，另一个是与圆的交点.探究:相交弦定理、割线定理、切割线定理和切线长定理这几个定理可统一记忆成一个定理：过圆内或圆外一点作圆的两条割线，则这Look at (看) Li Ming. He is from Guangzhou. He is thirteen years old. Now he is in Guangzhou Yuying Junior High School. He is in Class Five, Grade Eight. His telephone number is (020)7868-9688. Li Ming and Sally are friends. They are in the same class, but not the same age. She is twelve. She’s from Canada. Now Sally and her mom are in the same school. Her mom is a good teacher. Li Ming and Sally are good friends. 根据短文内容, 回答下列问题。 1. Where is Sally from? ______________________________ 2. Is Sally thirteen years old? ______________________________ 3. How old is Li Ming? ______________________________ 4. Are Li Ming and Sally good friends? ______________________________ 5. Where are Li Ming and Sally now? ______________________________