如图所示,AB为圆O的直径,CB,CD为圆O的切线,B,D为切点.
(1)求证:AD∥OC;
(2)若圆O的半径为2,求AD•OC的值.
(1)证明:连接BD,OD,
∵CB,CD是圆O的两条切线,
∴BD⊥OC,
又AB为直径,∴AD⊥DB,
∴AD∥OC.
(2)解:∵AD∥OC,∴∠DAB=∠COB,
∴Rt△BAD∽Rt△COB,
∴ADO
Tony has a new bike.It is different from .
已知:如图,AC和BD相交于点O,OA=OC,OB=OD.
(1)求证:AB∥CD.
(2)取线段OD的中点M,取线段OC的中点N,求MNAB的值.
-2的相反数的倒数是( )