设某钢珠直径<imgwidth="14"height="14"v:shapes="_x0000_i1251"src="http://wljy.whut.edu.cn:80/uploadfiles/word/xxdsb11.files/image322.png">服从正态分布<imgwidth="49"height="18"v:shapes="_x0000_i1252"src="http://wljy.whut.edu.cn:80/uploadfiles/word/xxdsb11.files/image324.png">,(单位:mm),其中<imgwidth="12"height="18"v:shapes="_x0000_i1253"src="http://wljy.whut.edu.cn:80/uploadfiles/word/xxdsb11.files/image276.png">为未知参数,从刚生产出的一大堆钢珠中随机抽出9个,求得样本均值<imgwidth="122"height="49"v:shapes="_x0000_i1254"src="http://wljy.whut.edu.cn:80/uploadfiles/word/xxdsb11.files/image326.png">,样本方差<imgwidth="170"height="40"v:shapes="_x0000_i1255"src="http://wljy.whut.edu.cn:80/uploadfiles/word/xxdsb11.files/image328.png">。则<imgwidth="12"height="18"v:shapes="_x0000_i1256"src="http://wljy.whut.edu.cn:80/uploadfiles/word/xxdsb11.files/image276.png">的极大似然估计值为()
②
<imgwidth="176"height="20"v:shapes="_x0000_i1257"src="http://wljy.whut.edu.cn:80/uploadfiles/word/xxdsb11.files/image330.png">
④
<imgwidth="58"height="20"v:shapes="_x0000_i1258"src="http://wljy.whut.edu.cn:80/uploadfiles/word/xxdsb11.files/image332.png">