9.设随机变量?服从瑞利(Rayleigh)分布，其密度函数为?2x?x2f(x)??2??2e,x?0 ???0,x?0试求：E?，D?，P(??E?).x2解：E????????x?f(x)dx????0x?x?2?2?2edx?2?2?????xE?2????x2?f(x)dx??0x2?x2?22?2?2edx? D??E?2?(E?)2?(2??22)?2?xP(??E?)?P(???2?2??2?)????x??edx?e4.2?2...
发布日期:2018-10-07 14:56:16