求下列每组数的最大公因数和最小公倍数．9和10 100和25 28和42．
直接写得数．﹣= += += +=﹣= ﹣= ﹣= +=1﹣= ﹣=．
计算下面各题．+﹣+++﹣﹣（+）
﹣= += ﹣= ﹣=+= ﹣= 1﹣= ﹣=﹣= +=
+ + + ．
递等式计算+= +=﹣= ﹣=1﹣= +﹣=1﹣+．
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