Gọi B = 1x2 + 2 x 3 + 3 x 4 + ... + 2016 x2017
3B = 3 x ( 1x2 + 2x3 + 3x4 + ... + 2016x2017)
= 1x2x3 + 2x3x3 + 3x4x3 + ... + 2016x2017x3 )
= 1x2x3 + 2x3x( 4-1) + 3x4x( 5 -2 ) + ... + 2016x2017x( 2018 - 2015)
= 1x2x3 + 2x3x4 - 1x2x3 + 3x4x5 - 2x3x4 + ... + 2016x2017x2018 - 2015x2016x2017
= 2016 x2017 x2018
B = 672 x2017 x2018
Mà A = \(\frac{672x2017x2018}{2017x2018}\)
= 672
Vậy A = 672
Tính nhanh:
\(1+\frac{1}{1x2}+\frac{1}{2x3}+\frac{1}{3x4}+...+\frac{1}{2017x2018}\)
C=\(\frac{1}{1x2}+\frac{1}{2x3}+\frac{1}{3x4}.............+\frac{1}{2017x2018}\)
1x2+2x3+3x4+4x5+...2016x2017
1/1x2+1/2x3+1/3x4+...+1/2015x2016+1/2016x2017
Tính : \(\frac{3}{1x3}+\frac{3}{2x3}+\frac{3}{3x4}+\frac{3}{4x5}+...+\frac{3}{2017x2018}\)
ai nhanh mik tick đang cần gấp
Tính a=1x2+2x3+3x4+...+99x100
Tính nhanh:. A = 1x2 + 2x3 + 3x4 + 4x5 + ... + 99x100.
Tính nhanh:.
A = 1x2 + 2x3 + 3x4 + 4x5 + ... + 99x100.
Cho A= 1x2+2x3+3x4+4x5+....+ 29x30
Tính Ax3=?
