x Turn on thread page Beta
 You are Here: Home >< Maths

# Integration, Differentiation, Stationary Points etc help please (: watch

1. Could I please have some guidance on this question?

Curve has equation y = 2x^3-6x.

(i) Show that the curve crosses the x-axis at the origin and the points (Sqrt3,0)
and (-Sqrt3,0)

(ii) Find dy/dx and stationary points on curve

(iii) Find d^2/dx^2 and stationary points

2. For the first question what is the value of y at the x-axis?

What do you know about the value of dy/dx at a stationary point? And what does the value of d^2y/dx^2 at a stationary point represent?
3. (Original post by Ben121)
For the first question what is the value of y at the x-axis?

What do you know about the value of dy/dx at a stationary point? And what does the value of d^2y/dx^2 at a stationary point represent?
I haven't been told what the value of y at the x-axis is; only the co-ordinates. Also for them both; need to find f(x) and f'(x).
4. (Original post by cee.jay)
I haven't been told what the value of y at the x-axis is; only the co-ordinates. Also for them both; need to find f(x) and f'(x).

At the x-axis the value of y is 0. Put that into your equation to work out what x is.
5. (Original post by cee.jay)
I haven't been told what the value of y at the x-axis is; only the co-ordinates. Also for them both; need to find f(x) and f'(x).
At the x axis y=0, so substitute that into the equation to get 0 = 2x^3-6x, then bring 6x to the other side to get 2x^3 = 6x, then find the values of x for which this is true

Spoiler:
Show
(obviously 0 is one of them, the other is x^3 = 3x or x^2 = 3, hence x = sqrt(3))).

The second part is just a simple differentiation, and to find the stationary points you set the derivative to 0 (since you are finding the points on the curve at which the gradient is 0 and the gradient is found by differentiation) and again find values of x which satisfy this, then for part 3 you simply take the derivative again. What does it mean by the stationary points of d^2y/dx^2 though? Does it want you to find the nature of the stationary points found in part ii)?

TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Updated: March 27, 2011
Today on TSR

### Loughborough better than Cambridge

Loughborough at number one

Poll
Useful resources

### Maths Forum posting guidelines

Not sure where to post? Read the updated guidelines here

### How to use LaTex

Writing equations the easy way

### Study habits of A* students

Top tips from students who have already aced their exams