139×137/138+137×1又1/138
=139×137/138+137×139/138
=2×﹙138+1﹚×137/138
=2×﹙138×137/138﹢137/138﹚
=2×﹙137+1﹣1/138﹚
=276-1/69
=275又68/69
139×137/138+137×1又1/138
=139×137/138+137×139/138
=2×﹙138+1﹚×137/138
=2×﹙138×137/138﹢137/138﹚
=2×﹙137+1﹣1/138﹚
=276-1/69
=275又68/69