1/3 = 2/6 = 2/(2x3) = 2/2 - 2/3
1/6 = 2/12 = 2/(3x4) = 2/3 - 2/4
...
2/x(x + 1) = 2/x - 2/(x +1)
Do đó:
1/3 + 1/6 + ... + 2/x(x+1) = 2/2 - 2/3 + 2/3 - 2/4 + ... +2/x - 2/(x + 1) = 2/2 - 2/(x+1)
suy ra 1 - 2/(x + 1) = 2013/2014
x= 4027
Tìm x biết 1/3+1/6+1/10+...+2/x(x+1)=2013/2014
1/3+1/6+1/10+...+2/x(x+1)=2011/2013. Tìm x
Tìm x biết 1/3 + 1/6 + 1/10 +.........+2/x. (x+1) = 2011/2013
Tính tổng: 1 x 2015 + 2 x 2014 + 3 x 2013 + … + 2014 x 2 + 2015 x 1
Tính A= 1/2 x 2/3 x 3/4 x ... x 2013/2014 x 2014/2015
( 2013 x 2014 x 2014 x 2015 + 2015 x 2016 ) x 1+1/3 - 1 và 1/3 )
A= (1-1/2)x(1-1/3)x(1-1/4)x.........x(1-1/2013)x(1-1/2014)
Tính A = ( 1- 1/2 ) x ( 1 - 1/3 ) x ( 1 - 1/4 ) x ... x ( 1 - 1/2013 ) x ( 1- 1/2014 )
A= (1-1/2)x(1-1/3)x(1-1/4)x.......x (1-1/2013)x(1-1/2014)=?
