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急,1998/1*2+1998/2*3+1998/3*4+1998/4*5+1998/5*6,
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急,1998/1*2+1998/2*3+1998/3*4+1998/4*5+1998/5*6,
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答案和解析
1998/1*2+1998/2*3+1998/3*4+1998/4*5+1998/5*6
=1998*(1/1*2+1/2*3+1/3*4+1/4*5+1/5*6)
=1998*(1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6)
=1998*(1-1/6)
=1998*5/6
=1665
=1998*(1/1*2+1/2*3+1/3*4+1/4*5+1/5*6)
=1998*(1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6)
=1998*(1-1/6)
=1998*5/6
=1665
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