1.AB是⊙O直径,AB=4,F是OB中点,弦CD⊥AB于F,则CD=_________

题目

1.AB是⊙O直径,AB=4,F是OB中点,弦CD⊥AB于F,则CD=_________
2.⊙O直径为8,弦AB＝42 ,则∠AOB＝＿＿＿＿＿.

答案