trả lời dùm mik đi!
Tính tổng
A= $\frac{1}{1.3}$ + $\frac{1}{3.5}$+ $\frac{1}{5.7}$+…+ $\frac{1}{2009.2021}$
A=(1- $\frac{2}{1.3}$)+(1- $\frac{2}{3.5}$)+…+(1- $\frac{1}{97-99)}$
Tìm n để A nguyên:
A= $\frac{3n+5}{n}$
B= $\frac{3n+5}{n-1}$
trả lời dùm mik đi! Tính tổng A= $\frac{1}{1.3}$ + $\frac{1}{3.5}$+ $\frac{1}{5.7}$+…+ $\frac{1}{2009.2021}$ A=(1- $\frac{2}{1.3}$)+(1- $\frac{2}{3
By Eliza
bài 1
a)ta có A = 1/1.3 +1/3.5+1/5.7+…….+1/2009.2021
=1/2(2/1.3 +2/3.5+2/5.7+…….+2/2009.2021
= 1/2(1/1-1/3+1/3-1/5+1/5-1/7+….+1/2009-1/2021)
=1/2 (1/1 -/2021)
= 1/2 (2021/2021-1/2021)
= 1/2 (2020/2021)
= 1010/2021