1abc的精选

问题详情：如果-1,a,b,c,-9成等比数列,那么(   )A.b＝3,ac＝9      B.b＝-3,ac＝9       C.b＝3,ac＝-9         D.b＝-3,ac＝-9【回答】解析:∵-1,a,b,c,-9成等比数列,∴b2＝ac,且ac＝9,a2＝-b＞0.∴b＜0.∴排除A、C、D...