已知随机变量<imgwidth="77"height="21"v:shapes="_x0000_i1134"src="http://wljy.whut.edu.cn/uploadfiles/word/xxdsb07.files/image174.png">,则随机变量<imgwidth="73"height="17"v:shapes="_x0000_i1135"src="http://wljy.whut.edu.cn/uploadfiles/word/xxdsb07.files/image176.png">的概率密度<imgwidth="54"height="25"v:shapes="_x0000_i1136"src="http://wljy.whut.edu.cn/uploadfiles/word/xxdsb07.files/image178.png">()
①
<imgwidth="131"height="49"v:shapes="_x0000_i1137"src="http://wljy.whut.edu.cn/uploadfiles/word/xxdsb07.files/image180.png">
②
<imgwidth="123"height="49"v:shapes="_x0000_i1138"src="http://wljy.whut.edu.cn/uploadfiles/word/xxdsb07.files/image182.png">
③
<imgwidth="88"height="49"v:shapes="_x0000_i1139"src="http://wljy.whut.edu.cn/uploadfiles/word/xxdsb07.files/image184.png">
④
<imgwidth="123"height="49"v:shapes="_x0000_i1140"src="http://wljy.whut.edu.cn/uploadfiles/word/xxdsb07.files/image186.png">