Zen increase

The maximum value is f(-2/3)=- 149/27, that is, all f (x).

So x0 is on (2, +∞), which is a single increasing interval; So by f (α) >; 0 can get α >; XO；

Then consider beta.

β=α-f(α)/f'(α)

Because f (α) >; 0, f'(α)>0, so β.

Then let x=x0 from the conclusion in (2).

0 & gtf(α)+f'(α)(x0-α)

-f(α)>f'(α)(x0-α)

-f(α)/f′(α)>x0-α

α-f(α)/f′(α)>x0

Namely β > x0

Over. If you have any questions, just say it.