$\text{1) Có: B = $\dfrac{(x-1)^2}{2}$}$
$\text{Thay x = -1}$
`⇒ B = \frac{(-1-1)^2}{2} = 4/2 = 2`
$\text{Vậy tại x = -1 thì B = 2}$
$\text{2) Có: P = A . B}$
`⇒ P = (\frac{1}{x-1} - \frac{1}{x+1}) . \frac{(x-1)^2}{2}` `(x \ne ±1)`
`P = \frac{x+1-x+1}{(x-1)(x+1)} . \frac{(x-1)^2}{2}`
`P = \frac{2}{(x-1)(x+1)} . \frac{(x-1)^2}{2}`
`P = \frac{x-1}{x+1}`
