Hello el123You have sign wrong - it should be - so this equation doesn't have any real roots. And so there's no point of inflexion.

Yes, there's a point of inflexion if .

Bear in mind that gives the rate of change (with respect to x) of , the gradient of .

So when , , the gradient of the curve, isincreasing; and when , isdecreasing.

But when the gradient of goes from increasing to decreasing (or the other way round). This is what a point of inflexion is - where the tangent touches the curve and cuts it at the same time (in other words has 3-point contact).

Grandad