如图,CD是⊙O的直径,弦AB⊥CD,P为垂足,AB=8cm,PD=2cm,则CP=______cm. 见图一
∵CD是⊙O的直径,弦AB⊥CD,P为垂足,AB=8cm, ∴AP=4,根据相交弦定理可知AP 2 =CP×PD, ∴16=2×CP, ∴CP=8cm.