27.我們規(guī)定:對(duì)于數(shù)對(duì)(a,b),如果滿(mǎn)足a+b=ab,那么就稱(chēng)數(shù)對(duì)(a,b)是“和積等數(shù)對(duì)”;如果滿(mǎn)足a-b=ab,那么就稱(chēng)數(shù)對(duì)(a,b)是“差積等數(shù)對(duì)”,例如:
×3,2-
.所以數(shù)對(duì)(
,3)為“和積等數(shù)對(duì)”,數(shù)對(duì)(2,
)為“差積等數(shù)對(duì)”.
(1)下列數(shù)對(duì)中,“和積等數(shù)對(duì)”的是
;“差積等數(shù)對(duì)”的是
.
①(-
,-2),②(
,-2),③(
,2).
(2)若數(shù)對(duì)(
,-2)是“差積等數(shù)對(duì)”,求x的值.
(3)是否存在非零有理數(shù)m,n,使數(shù)對(duì)(2m,n)是“和積等數(shù)對(duì)”,同時(shí)數(shù)對(duì)(2n,m)也是“差積等數(shù)對(duì)”,若存在,求出m,n的值,若不存在,說(shuō)明理由.