等比數列{an}是遞減數列,其前n項的積爲Tn,若T13＝4T9,則a8·a15等於( )A.±2 ... 問題詳情：等比數列{an}是遞減數列,其前n項的積爲Tn,若T13＝4T9,則a8·a15等於( )A.±2 B.±4 C.2 ...
