1/42+1/56+1/72
=1/(6×7)+1/(7×8)+1/(8×9)
=(1/6-1/7)+(1/7-1/8)+(1/8-1/9)
=1/6-1/9
=3/18-2/18
=1/18
答案：1/18
1\42+1\56+1\72等于多少?
1/42+1/56+1/72
=1/(6×7)+1/(7×8)+1/(8×9)
=(1/6-1/7)+(1/7-1/8)+(1/8-1/9)
=1/6-1/9
=3/18-2/18
=1/18
答案：1/18