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

* Hướng dẫn giải

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

$=\frac{\left(1-a\right)}{a\left(a+1\right)}:\frac{1-a}{{\left(a+1\right)}^2}$

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