Question

Tìm x

2/2x3+2/3x4+...+2/x(x+1)=2007/2009

Tính tổng

S=101/120+1/2x6+1/4x9+1/6x12+...1/36x57+1/38x60

Answer 1

= 2.(1 / 2.3 + 1 / 3.4 + ..... + 1 / x (x + 1) = 2007/2009

= 2.(1/2 - 1/3 + 1/3 - +.......+ 1/x - 1/x+1) = 2007/2009

= 2.( 1/2 - 1/x+1) = 2007/2009

= 1 - 1/x+1 =2007/2009

= 1/x+1 = 1/2009

=> x + 1 = 2009

=> x = 2008

Answer 2

Ta có: 2/2.3 + 2/3.4 + .... + 2/x.(x+1) = 2007/2009

=> 2.[1/2.3+1/3.4+.....+1/x.(x+1)]=2007/2009

=> 2.(1/2-1/3+1/3-1/4 + .... + 1/x - 1/x+1) = 2007/2009

=> 2.(1/2-1/x+1)=2007/2009

=>1/2 - 1/x+1 = 2007/2009 : 2

=> 1/2 - 1/x+1 = 2007/4018

=> 1/x+1 = 2007/4018 +1/2 

=> 1/x+1 = 

Answer 3

= 2.(1 / 2.3 + 1 / 3.4 + ..... + 1 / x (x + 1) = 2007/2009

= 2.(1/2 - 1/3 + 1/3 - +.......+ 1/x - 1/x+1) = 2007/2009

= 2.( 1/2 - 1/x+1) = 2007/2009

= 1 - 1/x+1 =2007/2009

= 1/x+1 = 1/2009

=> x + 1 = 2009

=> x = 2008

Answer 4

Ê Nobita Kun và Nguyễn Mai Phương  từ 2 mà đâu có 1 

Answer 5

= 2.(1 / 2.3 + 1 / 3.4 + ..... + 1 / x (x + 1) = 2007/2009

= 2.(1/2 - 1/3 + 1/3 - +.......+ 1/x - 1/x+1) = 2007/2009

= 2.( 1/2 - 1/x+1) = 2007/2009

= 1 - 1/x+1 =2007/2009

= 1/x+1 = 1/2009

=> x + 1 = 2009

=> x = 2008

Answer 6

Ta có: 2/2.3 + 2/3.4 + .... + 2/x.(x+1) = 2007/2009

=> 2.[1/2.3+1/3.4+.....+1/x.(x+1)]=2007/2009

=> 2.(1/2-1/3+1/3-1/4 + .... + 1/x - 1/x+1) = 2007/2009

=> 2.(1/2-1/x+1)=2007/2009

=>1/2 - 1/x+1 = 2007/2009 : 2

=> 1/2 - 1/x+1 = 2007/4018

=> 1/x+1 = 2007/4018 +1/2 

=> 1/x+1 =