齐次线性方程组<imgwidth="190"height="84"v:shapes="_x0000_i1169"src="http://wljy.whut.edu.cn/uploadfiles/word/xxds04.files/image200.png">的自由未知量为()
①
<imgwidth="40"height="26"v:shapes="_x0000_i1170"src="http://wljy.whut.edu.cn/uploadfiles/word/xxds04.files/image202.png">
②
<imgwidth="42"height="26"v:shapes="_x0000_i1171"src="http://wljy.whut.edu.cn/uploadfiles/word/xxds04.files/image204.png">
③
<imgwidth="42"height="26"v:shapes="_x0000_i1172"src="http://wljy.whut.edu.cn/uploadfiles/word/xxds04.files/image206.png">
④
<imgwidth="40"height="26"v:shapes="_x0000_i1173"src="http://wljy.whut.edu.cn/uploadfiles/word/xxds04.files/image208.png">