(1)连结BC,则∠OBC=∠D=45° ∠BOC=90° ∠OCB=45° OC=OB=k 点C坐标为(k,0);
(2)BC为⊙直径
BC=
=
k S ⊙A=π r 2= 8π
π(
k) 2=8π k = 4