二次型<imgwidth="324"height="28"v:shapes="_x0000_i1337"src="http://wljy.whut.edu.cn/uploadfiles/word/xxds05.files/image412.png">标准型为()
①
<imgwidth="92"height="28"v:shapes="_x0000_i1338"src="http://wljy.whut.edu.cn/uploadfiles/word/xxds05.files/image414.png">
②
<imgwidth="92"height="28"v:shapes="_x0000_i1339"src="http://wljy.whut.edu.cn/uploadfiles/word/xxds05.files/image416.png">
③
<imgwidth="104"height="28"v:shapes="_x0000_i1340"src="http://wljy.whut.edu.cn/uploadfiles/word/xxds05.files/image418.png">
④
<imgwidth="92"height="28"v:shapes="_x0000_i1341"src="http://wljy.whut.edu.cn/uploadfiles/word/xxds05.files/image420.png">