如图,l1∥l2∥l3,AB=AC,DF=10,那么DE=_________________.
若,则=_________________.
若tana=,则sina=___________________.
计算: ________________.
如图,小正方形的边长均为1,有格点△ABC,则sinC=( )
A. B. C. D.
如图所示:∠CAB=∠BCD,AD=2,BD=4,则BC=( )
A. B. C. 3 D. 6