Question

2x3/1+3x4/1+4x5/1+5x6/1+6x7/1+7x8/1+8x9/1+9x10/1+10x11/1=

Answer 1

解：①2x3/1+3x4/1+4x5/1+5x6/1+6x7/1+7x8/1+8x9/1+9x10/1+10x11/1
=6+12+20+30+42+56+72+90+110
=(6+12+72)+(20+30+90+110)+(42+56)
=90+250+98
=438
②如果楼主原意这样，那么解法不同：
1/2x3+1/3x4+1/4x5+1/5x6+1/6x7+1/7x8+1/8x9+1/9x10+1/10x11
=1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+6/1-1/7+1/7-1/8+1/8-1/9+1/9-1/10+1/10-1/11
=1/2-1/11
=9/22
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Answer 2

2x3/1+3x4/1+4x5/1+5x6/1+6x7/1+7x8/1+8x9/1+9x10/1+10x11/1
=1/2-1/3+1/3-1/4+1/4-1/5+...+1/10-1/11
=1/2-1/11
=9/22

Answer 3

2x3/1+3x4/1+4x5/1+5x6/1+6x7/1+7x8/1+8x9/1+9x10/1+10x11/1
=2/1-3/1+3/1-4/1+4/1-5/1+5/1-6/1+6/1-7/1+7/1-8/1+8/1-9/1+9/1-10/1+10/1-11/1
=2/1-11/1
=22/9