已知变量X和Y的协方差为-50, X的方差为180, Y的方差为20,其相关系数为()。[西安交大2008研]

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SQL Error: select id,body,options from ***_enewstiku where sourceid='30464' and id < 2461381 and id<>'2461381' order by id desc limit 5 SQL Error: select id,body,options from ***_enewstiku where sourceid='30464' and id > 2461381 and id<>'2461381' order by id asc limit 5