设随机变量X和Y相互独立,且都服从<imgwidth="61"height="25"v:shapes="_x0000_i1053"src="http://wljy.whut.edu.cn/uploadfiles/word/xxdsb09.files/image050.png">,若<imgwidth="172"height="21"v:shapes="_x0000_i1054"src="http://wljy.whut.edu.cn/uploadfiles/word/xxdsb09.files/image052.png">,其中<imgwidth="27"height="21"v:shapes="_x0000_i1055"src="http://wljy.whut.edu.cn/uploadfiles/word/xxdsb09.files/image054.png">为常数,则<imgwidth="28"height="25"v:shapes="_x0000_i1056"src="http://wljy.whut.edu.cn/uploadfiles/word/xxdsb09.files/image056.png">=()
①
<imgwidth="51"height="44"v:shapes="_x0000_i1057"src="http://wljy.whut.edu.cn/uploadfiles/word/xxdsb09.files/image058.png">
②
<imgwidth="51"height="44"v:shapes="_x0000_i1058"src="http://wljy.whut.edu.cn/uploadfiles/word/xxdsb09.files/image060.png">
③
<imgwidth="51"height="41"v:shapes="_x0000_i1059"src="http://wljy.whut.edu.cn/uploadfiles/word/xxdsb09.files/image062.png">
④
<imgwidth="50"height="41"v:shapes="_x0000_i1060"src="http://wljy.whut.edu.cn/uploadfiles/word/xxdsb09.files/image064.png">