Toán 1 / 2 x 4 + 1 / 4 x 6 + 1 / 6 x 8 + …. + 1 / 2018 x 2019 08/09/2021 By Alice 1 / 2 x 4 + 1 / 4 x 6 + 1 / 6 x 8 + …. + 1 / 2018 x 2019
Đặt biểu thức đó là A => 2A = 2/2×4+2/4×6+…+2/2018×2020 =1/2-1/4+1/4-1/6+…-1/2020 =1/2-1/2020 = 1009/2020 => A= 1009/2020:2 A= 1009/4040 Trả lời
A=$\frac{1}{2×4}$+$\frac{1}{4×6}$+$\frac{1}{6×8}$+….+$\frac{1}{2018×2019}$ Ax2=$\frac{2}{2×4}$+$\frac{2}{4×6}$+$\frac{2}{6×8}$+….+$\frac{2}{2018×2020}$ Ax2=$\frac{1}{2}$-$\frac{1}{4}$+$\frac{1}{4}$-$\frac{1}{6}$+ $\frac{1}{6}$-$\frac{1}{8}$+……+$\frac{1}{2018}$-$\frac{1}{2020}$ Ax2=$\frac{1}{2}$-$\frac{1}{2020}$ A=$\frac{1009}{2020}$:2 A=$\frac{1009}{4040}$ Trả lời
Đặt biểu thức đó là A
=> 2A = 2/2×4+2/4×6+…+2/2018×2020
=1/2-1/4+1/4-1/6+…-1/2020
=1/2-1/2020
= 1009/2020
=> A= 1009/2020:2
A= 1009/4040
A=$\frac{1}{2×4}$+$\frac{1}{4×6}$+$\frac{1}{6×8}$+….+$\frac{1}{2018×2019}$
Ax2=$\frac{2}{2×4}$+$\frac{2}{4×6}$+$\frac{2}{6×8}$+….+$\frac{2}{2018×2020}$
Ax2=$\frac{1}{2}$-$\frac{1}{4}$+$\frac{1}{4}$-$\frac{1}{6}$+ $\frac{1}{6}$-$\frac{1}{8}$+……+$\frac{1}{2018}$-$\frac{1}{2020}$
Ax2=$\frac{1}{2}$-$\frac{1}{2020}$
A=$\frac{1009}{2020}$:2
A=$\frac{1009}{4040}$