用简便方法计算 9999×7778+3333×6666 !!!!!!拜托了各位!!! !!!
用简便方法计算9999×7778+3333×6666!!!!!!拜托了各位!!!!!!!!!!!!!!!!!!!!!...
用简便方法计算 9999×7778+3333×6666 !!!!!!拜托了各位!!! !!!!!!!!!!!!!!!!!!
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9999×7778+3333×6666
= 9999×7778+9999×2222
=9999×(7778+2222)
=9999×10000
=99990000
2/3+2/(3*5)+...+2/(11*13) (偷一下懒哈)
=(1-1/3)+(1/3-1/5)+(1/5-1/7)+(1/7-1/9)+(1/9-1/11)+(1/11-1/13)
=1+(1/3-1/3)+(1/5-1/5)+(1/7-1/7)+(1/9-1/9)+(1/11-1/11)-1/13
=1+0+0+0+0+0-1/13
=1-1/13
=12/13
= 9999×7778+9999×2222
=9999×(7778+2222)
=9999×10000
=99990000
2/3+2/(3*5)+...+2/(11*13) (偷一下懒哈)
=(1-1/3)+(1/3-1/5)+(1/5-1/7)+(1/7-1/9)+(1/9-1/11)+(1/11-1/13)
=1+(1/3-1/3)+(1/5-1/5)+(1/7-1/7)+(1/9-1/9)+(1/11-1/11)-1/13
=1+0+0+0+0+0-1/13
=1-1/13
=12/13
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