问题
填空题
已知△ABC和△DBC所在的平面互相垂直，且AB=BC=BD，∠CBA=∠DBC=1200，则AB与平面ADC所成角的正弦值为
答案
根据题意建立直角坐标系，结合△ABC和△DBC所在的平面互相垂直，且AB=BC=BD，∠CBA=∠DBC=1200，得到线面角然后借助于直角三角形得到结论。
搜题请搜索小程序“爱下问搜题”
已知△ABC和△DBC所在的平面互相垂直，且AB=BC=BD，∠CBA=∠DBC=1200，则AB与平面ADC所成角的正弦值为
根据题意建立直角坐标系，结合△ABC和△DBC所在的平面互相垂直，且AB=BC=BD，∠CBA=∠DBC=1200，得到线面角然后借助于直角三角形得到结论。
Each nation has many volunteers(志愿者) who help to take care of others. They books to the people in hospitals or homes for the aged. Sometimes they just visit them and play games with them or listen to their .
Other young volunteers go and work in the homes of people who are sick or . They paint, clean up, their houses or do their shopping.
For boys who no longer have , there is an organization called Big Brothers. College students and other men take these boys to baseball games or fishing places and help them to get to know things that boys learn from their fathers.
Each city has a number of clubs boys and girls can go to play games or learn crafts (工艺). Some of these clubs organize short trips to the mountains, beaches, or other places of interest . Most of these clubs use high school and college students as volunteers because they are young enough to the names of boys and girls.
Volunteers believe that the happiest people in the world are those who help to i happiness to others.
| 小题1: | A．sell B．read C．throw D．show |
| 小题2: | A．voices B．speeches C．songs D．problems |
| 小题3: | A．young B．happy C．old D．hungry |
| 小题4: | A．pollute B．repair C．build D．remove |
| 小题5: | A．brothers B．sisters C．fathers D．mothers |
| 小题6: | A．usually B．never C．only D．seldom |
| 小题7: | A．which B．who C．when D．where |
| 小题8: | A．nearby B．faraway C．abroad D．home |
| 小题9: | A．report B．forget C．remember D．choose |
| 小题10: | A．cause B．bring C．take D．lend |