若二次型<imgwidth="394"height="28"v:shapes="_x0000_i1252"src="http://wljy.whut.edu.cn/uploadfiles/word/xxds05.files/image259.png">为正定二次型,则<imgwidth="16"height="20"v:shapes="_x0000_i1253"src="http://wljy.whut.edu.cn/uploadfiles/word/xxds05.files/image261.png">的取值范围为()
①
<imgwidth="80"height="48"v:shapes="_x0000_i1254"src="http://wljy.whut.edu.cn/uploadfiles/word/xxds05.files/image263.png">
②
<imgwidth="66"height="48"v:shapes="_x0000_i1255"src="http://wljy.whut.edu.cn/uploadfiles/word/xxds05.files/image265.png">
③
<imgwidth="54"height="48"v:shapes="_x0000_i1256"src="http://wljy.whut.edu.cn/uploadfiles/word/xxds05.files/image267.png">
④
<imgwidth="94"height="48"v:shapes="_x0000_i1257"src="http://wljy.whut.edu.cn/uploadfiles/word/xxds05.files/image269.png">