Cach lam chung: Dao ham va tim nghiem ptrinh y'=0. Khi do, nghiem cua ptrinh chinh la diem cuc tri cua hso.
a) $y' = \dfrac{x^2+8-(x+1)2x}{(x^2+8)^2}$
$y' = \dfrac{-x^2 -2x +8}{(x^2+8)^2}$
y'=0 <-> -x^2 - 2x + 8 =0 hay x=-4 hoac x=2.
Vay hso co 2 diem cuc tri la x=-4 hoac x=2.
b) $y' = \dfrac{(2x-2)(x-1)-(x^2-2x+3)}{(x-1)^2}$
$y' = \dfrac{x^2 -2x-1}{(x-1)^2}$
y'= <-> x^2 - 2x -1 = 0 hay x= $1 \pm \sqrt{2}$.
Vay hso co 2 diem cuc tri la $x = 1 -\sqrt{2}$ hoac $x = 1 + \sqrt{2}$.
