【单选题】
以下结论中不正确的是()
①
若存在可逆矩阵<imgwidth="18"height="20"v:shapes="_x0000_i1238"src="http://wljy.whut.edu.cn/uploadfiles/word/xxds05.files/image243.png">,使<imgwidth="70"height="24"v:shapes="_x0000_i1239"src="http://wljy.whut.edu.cn/uploadfiles/word/xxds05.files/image245.png">,则<imgwidth="18"height="18"v:shapes="_x0000_i1240"src="http://wljy.whut.edu.cn/uploadfiles/word/xxds05.files/image246.png">是正定矩阵
②
二次型<imgwidth="158"height="28"v:shapes="_x0000_i1241"src="http://wljy.whut.edu.cn/uploadfiles/word/xxds05.files/image248.png">是正定二次型
③
<imgwidth="14"height="16"v:shapes="_x0000_i1242"src="http://wljy.whut.edu.cn/uploadfiles/word/xxds05.files/image249.png">元实二次型正定的充分必要条件是<imgwidth="18"height="24"v:shapes="_x0000_i1243"src="http://wljy.whut.edu.cn/uploadfiles/word/xxds05.files/image233.png">的正惯性指数为<imgwidth="14"height="16"v:shapes="_x0000_i1244"src="http://wljy.whut.edu.cn/uploadfiles/word/xxds05.files/image249.png">
④
<imgwidth="14"height="16"v:shapes="_x0000_i1245"src="http://wljy.whut.edu.cn/uploadfiles/word/xxds05.files/image249.png">阶实对称矩阵<imgwidth="18"height="18"v:shapes="_x0000_i1246"src="http://wljy.whut.edu.cn/uploadfiles/word/xxds05.files/image246.png">正定的充分必要条件是<imgwidth="18"height="18"v:shapes="_x0000_i1247"src="http://wljy.whut.edu.cn/uploadfiles/word/xxds05.files/image246.png">的特征值全为正数