2/7 × 5/3 + 2/7 × 1/3 - 2/7 = 2/7 × 5/3 + 2/7 × 1/3 - 2/7 × 1 = 2/7 ×(5/3 + 1/3 - 1) = 2/7 × 1 = 2/7 数学中,通常会把后面的“× 1”省略不写,因为任何数与1相乘都是它本身,省略不会影响计算结果,但是...