1988+1989×19871988×1989−1=_.
问题描述:
=______. 1988+1989×1987 1988×1989−1
答
,1988+1989×1987 1988×1989−1
=
,1988+1989×(1988−1) 1988×1989−1
=
,1988+1989×1988−1989 1988×1989−1
=
,1988×1989−1 1988×1989−1
=1;
故答案为:1.