[考研]1990考研数三真题及解析

< 0;\rG : ¾ G : F" 0 ,\rFY (y)= ¿(+À, y) = lim F(x, y)= Á º\rx” [ 0, Fy<0.\r†‡Âqx,yÃ=ÄF(x,y) = Fx (x)FY (x).ÅÆX • ¶VÇÈz.\r(2 )ÅMX • y VÇÈz,67P\r<z = p{x> o.i,y> o.i} = p{x> o.i}p{y> o.i}\r= [1 - Fx(o.l)][l-4 (0.1)]= É .É =\rƒ4:(;<=>7>)\r@ABCFÊ?ËÌ>´`ÍŎÏ,pЙPc¢£Ñ@ÒÓÔÕMÖ×ËÌ>´`P\rc¢£,ØÙÚ(X)ÛЙ.Ü ËÌ>´`Ýqme 6 Þ?ÑOLßàá<lâ’ãä\rmeb ? `,—”ЙPc‘’`¢£.\rl X Mæç`èéyê,ë<‡PX ~ N ( " , s ) 8m = 72 , Ü (y2Þ?.67@Ö×\rY _ 72\rÕX-------- N (0,l).Ö×ËÌ>´·q¢£`Й¤U,P\r(J\rP{X>96} = 1-P{X 4 96} = 1 -Ú = 1- Ú ) = 0.023,\rÚ (} ) = 1 ?0.023 = 0.977.\r24\rìÛ@X 4 = 2,cr = 12,‚ X~N(72,122),\ra.\rP {6 0 < X < 8 4 } = P^ ¾ < B = 20)(1)-1 = 0.682.