第1个回答 2013-06-21
3/7 + 1/2 - 3/7
= 3/7 - 3/7 + 1/2
= 1/2
5/7 - 1/6 + 5/14
= 10/14 + 5/14 - 1/6
= 1 + 1/14 - 1 + 5/6
= 3/42 + 35/42
= 38/42
= 19/21
7/12 - ( 5/6 - 5/12 )
= 7/12 - 5/6 + 5/12
= 1 - 5/6
= 1/6
2/3 - 1/2 - 1/18
= 12/18 - 9/18 - 1/18
= 2/18
= 1/9
2x - 1/8 = 7/8
2x = 7/8 + 1/8
2x = 1
x = 1/2
x - 1/9 - 8/9 = 2
x - 1 = 2
x = 2 + 1
x = 3