y'=(x- 1)？ +3(x+ 1)(x- 1)？

y'=(x- 1)？ (x- 1+3x+3)

y'=2(x- 1)？ (2x+ 1)

Let y'=0 and x= 1 or-1/2.

When x ∝ ∞, 1/2 and y' < 0, y decreases monotonically.

When x ∝- 1/2, ∝∞, y' > 0, y monotonically increases.

(Note: when x= 1, it does not affect the monotonicity of this function, just like f-x) = x? , f ′ (0) = 0, but it is still monotonically increasing in R. )