Question

Giúp mình với, mai mình phải nộp bài rùiiiii plzzz

3/3.5 + 3/5.7 + 3/7.9 +...+ 1/x.(x+2)

Tìm x nha :)

Answer 1

Đặt \(A=\frac{3}{3.5}+\frac{3}{5.7}+...+\frac{3}{x\left(x+2\right)}\)(sửa đề)

\(\Rightarrow A=\frac{1}{2}.3.\left(\frac{1}{3}-\frac{1}{5}+\frac{1}{5}-\frac{1}{7}+...+\frac{1}{x}-\frac{1}{x+2}\right)\)

\(\Rightarrow A=\frac{3}{2}\left(\frac{1}{3}-\frac{1}{x+2}\right)\)

\(\Rightarrow A=\frac{1}{2}-\frac{3}{2x+4}\)