4/3-7/12+9/20-11/30+13/42-15/56
=4/3-(1/3+1/4)+(1/4+1/5)-(1/5+1/6)+(1/6+1/7)-(1/7+1/8)
=4/3-1/3-1/4+1/4+1/5-1/5-1/6+1/6+1/7-1/7-1/8
=4/3-1/3-1/8
=7/8.
4/3-7/12+9/20-11/30+13/42-15/56
=1+1/3-(1/3+1/4)+(1/4+1/5)-(1/5+1/6)+(1/6+1/7)-(1/7+1/8)
=1-1/8
=7/8
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