矿井里的升降机,由静止开始匀加速上升,经5s速度达到6m/s后,又以此速度匀速度上升10s,然后匀减速上升,又经10s停在井口.求矿井的深度.
解:加速位移: x1=v2⋅t1=62×5
cos210°的值为( )
判断对错.
7+6-8=5
——Did the book give the ___________ you needed?——Yes. But ____________ it, I had to read the whole book.
设变量x,y满足约束条件y≥0x-y+1≥0x+y-3≤0,则z=2x+y的最大值为 ( )