166*167分之166 怎样算简便还有一题 1/2+1/6+1/12+1/20+1/30+1/42+1/56 1998*(1/11-1/2009)+11*(1/1998-1/2009 )-2009*(1/11+1/1998)+3 简便计算 我想要弄明白

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166*167分之166怎样算简便还有一题1/2+1/6+1/12+1/20+1/30+1/42+1/561998*(1/11-1/2009)+11*(1/1998-1/2009)-2009*(1/1

166*167分之166 怎样算简便还有一题 1/2+1/6+1/12+1/20+1/30+1/42+1/56 1998*(1/11-1/2009)+11*(1/1998-1/2009 )-2009*(1/11+1/1998)+3 简便计算 我想要弄明白
166*167分之166 怎样算简便
还有一题 1/2+1/6+1/12+1/20+1/30+1/42+1/56 1998*(1/11-1/2009)+11*(1/1998-1/2009 )-2009*(1/11+1/1998)+3 简便计算 我想要弄明白

166*167分之166 怎样算简便还有一题 1/2+1/6+1/12+1/20+1/30+1/42+1/56 1998*(1/11-1/2009)+11*(1/1998-1/2009 )-2009*(1/11+1/1998)+3 简便计算 我想要弄明白
166*167分之166
=(167-1)×166/167
=1-166/167
=1/167
1/2+1/6+1/12+1/20+1/30+1/42+1/56
=1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7+1/7-1/8
=1-1/8
=7/8
1998*(1/11-1/2009)+11*(1/1998-1/2009 )-2009*(1/11+1/1998)+3
=1998/11-1998/2009+11/1998-11/2009-2009/11-2009/1998+3
=(1998/11-2009/11)-(1998/2009+11/2009)+(11/1998-2009/1998)+3
=-11/11-2009/2009-1998/1998+3
=-3+3
=0