设，则（为常数）的值．https://img-ph-mirror.nosdn.127.net/OCKSU6xXGRmrhqyAjxCsLQ==/6608185829214053227.pnghttps://img-ph-mirror.nosdn.127.net/JkqlqFql5XkrAZfdvWFndg==/6608888417143176694.pnghttps://img-ph-mirror.nosdn.127.net/twXY8ldkHYPX6F401pfEHA==/6597409515751723222.png

(10). 设某种元件的寿命 \( X\sim N(\mu ,\sigma ^2) \)，其中参数 \( \mu ,\sigma^2 \) 未知，为估计平均寿命 \( \mu \) 及方差 \( \sigma^2 \)，随机抽取7只元件得寿命为(单位:小时)

设随机变量 X 的数学期望和方差均是6，那么 。https://img-ph-mirror.nosdn.127.net/z93FDkyMmust_IrJDqVuyQ==/6631762657048804378.png

设集合, A上的关系 , , 则 = ________________________, =____________________________, =________________________.https://img-ph-mirror.nosdn.127.net/Ir_BnXKpLuVzUv8qV7DePQ==/2596043710222405203.pnghttps://img-ph-mirror.nosdn.127.net/W0kxC_oqhCGcgMXSIxmrNA==/6608671813352373524.pnghttps://img-ph-mirror.nosdn.127.net/HMPOvS1yBV1g-eoGPCLtlw==/6631646108818998910.pnghttps://img-ph-mirror.nosdn.127.net/4eO2QDOmozl6k9VETPbb4w==/6608268292585874055.pnghttps://img-ph-mirror.nosdn.127.net/6cXPP6rjlU7ck0eZJzL6Bg==/1237645472697074344.pnghttps://img-ph-mirror.nosdn.127.net/HsOfJ7hBkTkJ0DABRo-H4g==/6597830628705090333.pnghttps://img-ph-mirror.nosdn.127.net/0Vf76qI2ztdq1ovUkaFePw==/6608268292587415060.pnghttps://img-ph-mirror.nosdn.127.net/LuQvCoi51wQzU--Fomwenw==/6597909793542286834.png

基质适宜的pH值为（ ），基质pH=（ ）较好。（ ）。 A: pH值为5.5～7.5，基质pH=6～7.5 B: pH值为5.5～7.5，基质pH=6～7 C: pH值为5～7，基质pH=6～7 D: pH值为5.5～7.5，基质pH=6.5～7