139x137/138+137x1又1/138的简便运算 答案上是275又68/69

139 × 137/138 + 137 × 1又1/138
=139 × 137/138 + 137 ×139/138
=2 ×139 ×137/138
=2 ×(138+1) ×(138-1)/138
=2 ×(138²-1)/138
=2 ×138 - 1/69
=275又68/69

=139×137/138+137×(1+1/138)
=139×137/138+137×1+137×1/138
=(139+1)×137/138+137
=(138+2)×137/138+137
=138×137/138+2×137/138+137
=137+137+137/69
=274+1+68/69
=275又68/69

139x137/138+137x1又1/138
=（138+1）×137/138+137+137/138
=137+137/138+137+137/138
=274+137/69
=274+1又68/69
=275又68/69