A:an underground lake was discovered
B:there was an underground lake discovered
C:a lake was discovered underground
D:the workers discovered an underground lake
要给体温计消毒可采用下面的哪种方法( )。
如图,在△ABC中,I是内心,O是AB边上一点,⊙O经过B点且与AI相切于I点.
(1)求证:AB=AC;
(2)若BC=16,⊙O的半径是5,求AI的长.
如图所示,电源电压恒为12V,电阻R1为20Ω,当开关S闭合后,电压表的示数为8V,求: