簽到天數: 4939 天 [LV.Master]伴壇終老
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myself|2012-1-20 01:12
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a x a = ( 1 + 3 + 5 + .... + 99 ) = ( 99 + 97 +95 + ... + 1 )
2 x a x a = ( 1 + 3 + 5 + .... + 99 ) + ( 99 + 97 +95 + ... + 1 )
= ( 1 + 99 ) + ( 3 + 97 ) + ( 5 + 95 ) + ... + ( 99 + 1 )
= 50 x 100
a x a = 50 x 50
a = 50 |
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