A:Yes, I could
B:Just a moment
C:That,s right
D:No problem
先化简,再求值:(x+y)(x-y)-x(x-2y),其中x=13,y=3.
如图.AB是⊙O的直径,E是弧BC的中点,OE交BC于点D,OD=3,DE=2,则AD的长为( ).