Inflexion points (1 Viewer)

[Joshmosh2]

If I find the second derivative for a function, and end up with something like
y'' = 6x -7
How can I find out the points of inflexion?
Also, how can I determine whether they are concave up or down?

For finding the points, I am assuming y'' = 0 and solve for x
and from there, depending on whether the the solution for x is positive or negative, that will determine concave up or down?
Not entirely sure.
Thanks.

 

[randomly_generated]

Yes for possible points of inflection, solve second diff = 0 and then determine concavity

 

[Joshmosh2]

Yes for possible points of inflection, solve second diff = 0 and then determine concavity

thanks, and also, to find the y-coordinate, sub into f(x) or f'(x)?

 

[Stygian]

for the y coordinate sub into f(x)

 

[randomly_generated]

for the y coordinate sub into f(x)

This

 

[randomly_generated]

Subbing x into y' is meaningless in hsc maths

 

[ConorDevaney]

when proving it a point of inflexion, you have to test for values above and below the "possible point go inflexion", otherwise you won't receive the full marks of the question