题目

若等腰直角三角形的外接圆半径的长为2，则其内切圆半径的长为（ ） A． B．2﹣2 C．2﹣D．﹣2 答案：B【分析】由于直角三角形的外接圆半径是斜边的一半，由此可求得等腰直角三角形的斜边长，进而可求得两条直角边的长；然后根据直角三角形内切圆半径公式求出内切圆半径的长． 【解答】解：∵等腰直角三角形外接圆半径为2， ∴此直角三角形的斜边长为4，两条直角边分别为2， ∴它的内切圆半径阅读理解。     Robert Spring, a 19th century forger (伪造者), was so good at his profession that he was able to make his living for 15 years by selling false signatures of Americans. Spring was born in England in 1813 and arrived in Philadelphia in 1858 to open a bookstore. At first he became rich by selling his small but real collection of early U.S. autographs (手稿). Discovering his ability at copying handwriting, he began imitating signatures of George Washington and Ben Franklin and writing them on the title pages of old books. To lessen the chance of detection (察觉), he sent his forgeries to England and Canada for sale.     Forgers have a hard time selling their products. A forger can't deal with a respectable buyer but people who don't have much knowledge in the field. Forgers have many ways to make their work look real. For example, they buy old books to use the aged paper of the title page, and they can treat paper and ink with chemicals.     In Spring's time, right after the Civil War, Britain was still fond of the Southern states, so Spring invented a respectable maiden lady known as Miss Fanny Jackson, the only daughter of General "Stonewall" Jackson. For several years Miss Fanny's financial problems forced her to sell a great number of letters and manuscripts. Spring had to work very hard to satisfy the demand. All this activity did not prevent Spring from dying in poverty, leaving sharp-eyed experts the difficult task of separating his forgeries from the originals.1. Why did Spring sell his false autographs in England and Canada?A. There was a greater demand there than in America.B. There was less chance of being detected there.C. Britain was Spring's birthplaceD. The prices were higher in England and Canada.2. After the Civil War, there was a great demand in Britain for             . A. Southern money           B. signatures of George Washington and Ben FranklinC. Southern manuscripts and letters      D. Civil War battle plans3. Robert Spring spent 15 years          .A. running a bookstore in Philadelphia      B. keeping in touch with Miss Fanny JacksonC. as a forger                          D. as a respectable dealer4. According to the passage, forgeries are usually sold to        .A. sharp-eyed experts   B. persons who aren't expertsC. book dealers        D. owners of old books