y' = 3x2 +2x +1
a. y' <= 6
<=> 3x2 + 2x +1 <=6
<=.> \(\dfrac{-5}{3}\) <= x <= 1
B. K=6
<=> 3x2 + 2x +1 = 6
<=> \(\left[{}\begin{matrix}x=1\\x=\dfrac{-5}{3}\end{matrix}\right.\)
với x= 1 => y= -2
vập pttt: y = 6 (x-1) -2
<=> y = 6x - 8
với x=\(\dfrac{-5}{3}\) => y = \(\dfrac{-230}{27}\)
vập pttt : y= 6( x + \(\dfrac{5}{3}\) ) - \(\dfrac{230}{27}\)
<=> y = 6x + \(\dfrac{40}{27}\)