1/1x2+1/2x3+1/3x4+.1/49x50
=1-1/2+1/2-1/3+1/3-1/4++.1/49-1/50
=1-1/50
=49/50
3/4+3/4x7+3/7x10+3/10x13
=1-1/4+1/4-1/7+1/7-1/10+1/10-1/13
=1-1/13
=12/13
1/3+1/3x5+1/5x7+1/7x9+1/9x11
=1/2×(1-1/3+1/3-1/5+1/5-1/7+1/7-1/9+1/9-1/11)
=1/2×(1-1/11)
=5/11
1/2=1/2x1=1-1/2 ,1/6=1/2x3=1/2-1/3,1/12=1/3x4=1/3-1/4.
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相关问题
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