Show that $b=8a^2$ The point of inflection on the curve $y=x^3-ax^2-bx+c$, is a stationary point of inflexion. I do not understand the meaning of 'stationary', how can it be shown that $b=8a^2$?

I did not understand properly.For an inflection point

$$ f''(x)=6x-2a =0 \implies x= a/3 $$

Since at a stationary point slope should also vanish,

$$ f'(x)=3x^2-2ax-b = 3{\left(\frac{a}{3}\right)}^2-2a{\left(\frac{a}{3}\right)} -b =0 $$ or

$$ \frac{a^2}{3}+b=0 $$

is not what was asked to show.