如图,AB为⊙O的直径,PD切⊙O于点C,交AB的延长线于D,且CO=CD,则∠PCA=( )
A:30°
B:45°
C:60°
D:67.5°
— How was your trip?
— Very good. We enjoyed ______.
已知双曲线x2a2-y2=1(a>0)的一条渐近线为3x+y=0,则a=____ .
春秋第一霸主是楚庄王。
错误:____;改正:____
如图,用手指压塑料尺,可以观察到尺发生弯曲.对于此现象,说法错误的是( )