7/8*[6/7-(1/21+3/7)]

问题描述:

7/8*[6/7-(1/21+3/7)]

7/8*[6/7-(1/21+3/7)]
=7/8*[6/7-10/21]
=7/8*[18/21-10/21]
=7/8*8/21
=1/3