有一列数：l，1989，l988，l，l987，…．从第三个数起，每一个数都是它前面两个数中大数减小数的差．那么第1989个数是多少?
先看清左右两题之间的关系，再写出得数．========
算一算．×3=×4=×2==÷3=÷4=÷2=÷2=
开火车．
直接写得数===== 9×= 0.8﹣==
× 6×8+÷ 2.4× 1﹣72%
=
=
=
=
=
=
=
=
×3=
×4=
×2=
=
÷3=
÷4=
÷2=
÷2=
=
=
=
=
= 9×
= 0.8﹣
=
=
×
6
×8
+
÷
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