Cach giai chung: Tim dao ham va tim nghiem ptrinh y'=0. Khi do, nghiem cua ptrinh chinh la cac diem ctri cua ham so.
c)$y = \dfrac{x^2 + x-5}{x+1}$
$y' = \dfrac{(2x+1)(x+1) - (x^2 + x -5)}{(x+1)^2} = \dfrac{x^2 +2x + 6}{(x+1)^2}$
y'=0 <-> $x^2 +2x + 6 = 0$.
Ptrinh tren vo nghiem. Vay hso ko co diem cuc tri.
d) $y = \dfrac{x^2 - 8x + 16}{x^2 - 2x + 5}$
$y' = \dfrac{(2x-8)(x^2-2x+5) - (x^2-8x+16)(2x-2)}{(x^2-2x+)^2}$
$y' = \dfrac{6x^2 -22x -8}{(x^2-2x+)^2}$
y'=0 <-> tu so =0 hay 6x^2 -22x -8=0 <-> x=4 hoac x=-1/3.
Vay hso co 2 diem cuc tri la x=4 va x=-1/3.
