二次型<imgwidth="246"height="28"v:shapes="_x0000_i1258"src="http://wljy.whut.edu.cn/uploadfiles/word/xxds05.files/image271.png">标准型为()
①
<imgwidth="126"height="46"v:shapes="_x0000_i1259"src="http://wljy.whut.edu.cn/uploadfiles/word/xxds05.files/image273.png">
②
<imgwidth="126"height="46"v:shapes="_x0000_i1260"src="http://wljy.whut.edu.cn/uploadfiles/word/xxds05.files/image275.png">
③
<imgwidth="122"height="28"v:shapes="_x0000_i1261"src="http://wljy.whut.edu.cn/uploadfiles/word/xxds05.files/image277.png">
④
<imgwidth="130"height="46"v:shapes="_x0000_i1262"src="http://wljy.whut.edu.cn/uploadfiles/word/xxds05.files/image279.png">