1*2/1+2*3/1+3*4/1+.+2004*2005/1=1*3/1+3*5/1+5*7/1+.+49*51/1=
来源:学生作业帮助网 编辑:作业帮 时间:2024/07/14 13:34:50
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1*2/1+2*3/1+3*4/1+.+2004*2005/1=1*3/1+3*5/1+5*7/1+.+49*51/1=
1*2/1+2*3/1+3*4/1+.+2004*2005/1=
1*3/1+3*5/1+5*7/1+.+49*51/1=
1*2/1+2*3/1+3*4/1+.+2004*2005/1=1*3/1+3*5/1+5*7/1+.+49*51/1=
这是裂项法:
1*2/1+2*3/1+3*4/1+.+2004*2005/1
=1-2/1+2/1-3/1+3/1-4/1+……+2004/1-2005/1
=1-2005/1
=2005/2004
1*3/1+3*5/1+5*7/1+.+49*51/1
=2/1*(1-3/1+3/1-5/1+5/1-7/1+……+49/1-51/1)
=2/1*(1-51/1)
=2/1*51/50
=51/25