137 1
问题描述:
137 1
139X —— — 137X ——
138 138
答
139×137/138-137×1/138
=(139-1)×137/138
=138×137/138
=137139为什么要减1?139×137/138-137×1/138=139×137/138-137/138=(139-1)×137/138=138×137/138=137 139个137/138减去1个137/138=(139-1)个137/138