Rút gọn biểu thức sau: (2/a^2 + a - 2/a + 1) : 1 - a/a^2 + 2a + 1

* Hướng dẫn giải

$$\begin{gathered} B=\left(\frac{2}{a^2+a}-\frac{2}{a+1}\right):\frac{1-a}{a^2+2a+1} \\ B=\frac{2\left(1-a\right)}{a\left(a+1\right)}:\frac{1-a}{{\left(a+1\right)}^2} \\ B=\frac{2\left(1-a\right)}{a(a+1)}\cdot \frac{{\left(a+1\right)}^2}{1-a} \\ B=\frac{2a+2}{a} \end{gathered}$$