easy mà
=2.(1/1.2+1/2.3+...+1/1999.2000)
=2.(1/1-1/2+1/2-1/3+....1/1999-1/2000)
=2.(1-1/2000)
=2.1999/2000
=3998/2000=... tự rút gọn :D
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easy mà
=2.(1/1.2+1/2.3+...+1/1999.2000)
=2.(1/1-1/2+1/2-1/3+....1/1999-1/2000)
=2.(1-1/2000)
=2.1999/2000
=3998/2000=... tự rút gọn :D
Tính: S = 1x2-2x3+3x4-4x5+5x6-6x7+...-1998x1999+1999x2000
A=2/1x2 + 2/2x3 + 2/3x4 + ... + 2/9x10
c = 2 /1x2 + 2/2x3 +2/3x4 +2/4x5 +2/5x6 + 2/6x7
tính:2/1x2+2/2x3+2/3x4+2/4x5+...+2/99x100
Tìm y
y x ( 2/1x2 + 2 / 2x3 + 2 / 3x4 +... + 2/99x100 ) = 198/100
tinh nhanh 2/1X2+2/2X3 +2/3X4+2/4X5 + ............ +2/99X100
2/1x2 + 2/2x3 + 2/3x4 + 2/4x5 + ... + 2/19x20 = ?
C=\(\dfrac{2}{1x2}\)+\(\dfrac{2}{2x3}\)+\(\dfrac{2}{3x4}\)+...+\(\dfrac{2}{2018x2019}\)+\(\dfrac{2}{2019x2020}\)
so sánh S và 2019/2010 biết S là: 2/1x2 +2/2x3 + 2/3x4 +...+2/2020x2021