题目

Not all people can afford to buy expensive books. There are Sending libraries where people, old and young, can borrow books if they are members. The largest library in Singapore is the National Library at Stamford Road. More than thousands of books can be found. Most of them are English books although there are also some Chinese and Malay readers. You can borrow books from the library if you are a member. To be a member you have to pay a certain fee. After you have paid the fee, you are given a card and you can use this card to borrow books for three weeks at a time. Students do not need to pa13．在数学实验课上，李静同学剪了两张直角三角形纸片，进行了如下的操作：操作一：如图1，将Rt△ABC纸片沿某条直线折叠，使斜边两个端点A与B重合，折痕为DE．（1）如果AC=5cm，BC=7cm，可得△ACD的周长为12cm；（2）如果∠CAD：∠BAD=1：2，可得∠B的度数为36°；操作二：如图2，李静拿出另一张Rt△ABC纸片，将直角边AC沿直线CD折叠，使点A与点E重合，若AB=10cm，BC=8cm，请求出BE的长．