Đặt 2x + 1 = a ĐK a khác 0 ; -1 pt \(1+\frac{1}{a^2}+\frac{1}{\left(a+1\right)^2}=4\)=> \(\frac{a^2\left(a+1\right)^2+\left(a+1\right)^2+a^2}{a^2\left(a+1\right)^2}=4\)=> \(\frac{a^2\left(a^2+2a+1+1\right)+\left(a+1\right)^2}{a^2\left(a+1\right)^2}=4\)=> \(\frac{a^4+2a^2\left(a+1\right)+\left(a+1\right)^2}{a^2\left(a+1\right)^2}=4\)=> \(\frac{\left(a^2+a+1\right)^2}{a^2\left(a+1\right)^2}=4\)=> \(\frac{a^2+a+1}{a\left(a+1\right)}=2\) hoặc \(\frac{a^2+a+1}{a\left(a+1\right)}=-2\)Giải a tìm x Câu trả lời: Đặt 2x + 1 = a ĐK a khác 0 ; -1 pt \(1+\frac{1}{a^2}+\frac{1}{\left(a+1\right)^2}=4\)=> \(\frac{a^2\left(a+1\right)^2+\left(a+1\right)^2+a^2}{a^2\left(a+1\right)^2}=4\)=> \(\frac{a^2\left(a^2+2a+1+1\right)+\left(a+1\right)^2}{a^2\left(a+1\right)^2}=4\)=> \(\frac{a^4+2a^2\left(a+1\right)+\left(a+1\right)^2}{a^2\left(a+1\right)^2}=4\)=> \(\frac{\left(a^2+a+1\right)^2}{a^2\left(a+1\right)^2}=4\)=> \(\frac{a^2+a+1}{a\left(a+1\right)}=2\) hoặc \(\frac{a^2+a+1}{a\left(a+1\right)}=-2\)Giải a tìm x