题目

在Rt△ABC中，∠C=90°，若cosA=，BC=24，则AC=________． 答案：10分析：根据余弦的定义得到cosA==，这样可设CA=5x，AB=13x，然后根据勾股定理计算出BC=12x，利用BC=24可解得x=2，即可得到AC的长．解答：解：如图，∵cosA==，∴设CA=5x，AB=13x，∴BC===12x，而BC=24，∴12x=24，∴x=2，∴AC=5×2=10．故答案为10．点评：本题考查了锐角三角函数的定义：在直角三角形中，一锐角的余短文改错。     假定英语课上英语老师要求同桌之间互相修改作文，请你修改你同桌的以下作文。文中共有10处语言错误，每句中最多有两处。错误涉及一个单词的增加、删除或修改。     删除：把多余的词用斜线（\）划掉。     增加：在缺词处加一个漏字符号（∧），并在该词下面写出该加的词。     修改：在错的词下划一横线，在该词下面写出修改后的词。      注意：1、每处错误及修改均仅限一词。                 2、只允许修改10处，多者（从11处起）不计分。      It was almost five years since I began to learn English. I'm glad to say I'm getting along well with it. Butfirst I came across a lot of difficulties. I couldn't pronounce English sounds good, nor could I remember thewords I had learned. In class,I couldn't understand that the teacher had said. I almost lost my heart when theteacher told me,"Keeping on and you will do well" I was great encouraged. I started working hard at English. With the help of his and my classmates, I made some progresses. I'm very pleased, but I will work harder. ________________________________________________________________________________________