Chủ đề này có 1 trả lời

[BurakkuYokuro11]

Cho $1-\frac{1}{3}+\frac{1}{5}-\frac{1}{7}+\frac{1}{9}-\frac{1}{11}+...=\frac{\pi }{4}$

Tìm x : $\frac{1}{1.3}+\frac{1}{5.7}+\frac{1}{9.11}+...=\frac{\pi }{x}$

 

[ThinhThinh123]

$2.(\frac{1}{1.3}+\frac{1}{5.7}+\frac{1}{9.11}+...)=2.(\frac{\pi }{x})$

$ <=>1-\frac{1}{3}+\frac{1}{5}-\frac{1}{7}+\frac{1}{9}-\frac{1}{11}+...=2.(\frac{\pi }{x})$

$=> \frac{\pi }{4}=2.(\frac{\pi }{x})=> x=8$