问题
填空题
已知Rt△ABC的斜边BC=5，则
|
答案
设AC=b，AB=c，
原式=5bcos（180°-C）+0+5ccos（180°-B）
=-5bcosC-5ccosB
=-5（asinA+csinC）
=-5（2Rsin2A+2Rsin2B）
=-5×2R，
∵R是三角形外接圆的半径，
∴2R=5，
∴原式=-25，
故答案为：-25．
搜题请搜索小程序“爱下问搜题”
已知Rt△ABC的斜边BC=5，则
|
设AC=b，AB=c，
原式=5bcos（180°-C）+0+5ccos（180°-B）
=-5bcosC-5ccosB
=-5（asinA+csinC）
=-5（2Rsin2A+2Rsin2B）
=-5×2R，
∵R是三角形外接圆的半径，
∴2R=5，
∴原式=-25，
故答案为：-25．
| 阅读理解。 | |||||
| |||||
| 1. If you want to know something about Japan, which of the following programs would be the best one? | |||||
| A. Weather Report. B. China 2001. C. Around the World . D. Animal World. | |||||
| 2. If you are a basketball fan, you may watch TV at _______. | |||||
| A. 19: 00 on Channel 2 B. 19: 40 on Channel 1 C. 20: 20 on Channel 2 D. 21: 15 on Channel 1 | |||||
| 3. How long does the TV play "A Big Family" last? | |||||
| A. 30 minutes. B. 50 minutes. C. 90 minutes. D. 100 minutes. | |||||
| 4. You can watch _______ if you want to learn English on TV. | |||||
| A. English News B. English Classroom C. English for Today D. all the above | |||||
| 5. You should wait until _______ if you want to know the programs of next week. | |||||
| A. 21: 55 B. 22: 05 C. 21: 00 D. 21: 45 |