F = 42x4 + 44x6 + 46x8 +....+42008x2010

2 câu trả lời

F=42.4+44.6+46.8+...

F = 2 . ( 2/( 2 . 4 ) + 2/( 4 . 6 ) + 2/( 6 . 8 ) + .... + 2/( 2008 . 2010 ) )

F = 2 . ( 1/2 - 1/4 + 1/4 - 1/6 + 1/6 - 1/8 + .... + 1/2008 - 1/2010 )

F = 2 . ( 1/2 - 1/2010 )

F = 2 . ( 1005/2010 - 1/2010 )

F = 2 . 502/1005

F = 1004/1005

Vậy , F = 1004/1005 .

F = 4/{2.4} + 4/{4.6} + 4/{6.8} + ... + 4/{2008.2010}

F = 2. ( 2/{2.4} + 2/{4.6} + 2/{6.8} + ... + 2/{2008.2010} )

F = 2. ( 1/2 - 1/4 + 1/4 - 1/6 + 1/6 - 1/8 + ... + 1/2008 - 1/2010 )

F = 2. ( 1/2 - 1/2010 )

F = 2. 502/1005

F = 1004/1005