A:had managed
B:would managed
C:have managed
D:managed
如图所示,四边形ABCD中,∠B=90°,AB=2,CD=8,AC⊥CD,若sin∠ACB=13,则cos∠ADC=____.
已知sinθ<0,tanθ>0,则1-sin2θ化简的结果为( )