原式
=21/17*(2+2/3-3/4)+(11/12)*21/17
=21/17*(2+2/3-3/4+11/12)
=21/17*(2+8/12-9/12+11/12)
=21/17(2-1/12+11/12)
=21/17(2+10/12)
=21/17(2+5/6)
=21/17*17/6
=21/6
=7/2能简单一点吗哦