Be quick,or we won't catch the first bus on time. (改为同义句)
____ ____,or we won't catch the first bus on time.
小红做了9朵花,小方做了3朵花,一共做了几朵花?
麦克斯韦预言了电磁波的存在,赫兹用实验证实了这一预言.电磁波按照波长由长到短排列依次是:无线电波、红外线、可见光、紫外线、____、γ射线.南京调频音乐电台的播放频率是105.8MHz,已知电磁波的传播速度为3.0×108m/s,则该电台信号的波长是____m.
如图,为估算某河的宽度,在河对岸选定一个目标点A,在近岸取点B,C,D,使得AB⊥BC,CD⊥BC,点E在BC上,并且点A,E,D在同一条直线上.若测得BE=20m,CE=10m,CD=20m,则河的宽度AB等于( )
已知:4x2-1=Ax-1+Bx+1是一个恒等式,则A=____ ,B=____ .