③ 存在常数<imgwidth="27"height="21"v:shapes="_x0000_i1179"src="http://wljy.whut.edu.cn/uploadfiles/word/xxdsb09.files/image260.png">使<imgwidth="116"height="27"v:shapes="_x0000_i1180"src="http://wljy.whut.edu.cn/uploadfiles/word/xxdsb09.files/image262.png">