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问题: 计算题

4/3-12/7+9/20-11/30+13/42-15/56+17/72

解答:

4/3-12/7+9/20-11/30+13/42-15/56+17/72
=(1+3)/(1*3)-(3*4)/(3+4)+(4+5)/(4*5)-(5+6)/(5*6)+(6+7)/(6*7)-(7+8)/(7*8)+(8+9)/(8*9)
=1/3+1/1-(3*4)/(3+4)+1/5+1/4-1/6-1/5+1/7+1/6-1/8-1/7+1/8+1/9
如果12/7是7/12,原来式子得
1+1/9=10/9