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

# Help with C3 Differentiation Please watch

1. For each, Find the co-ordinates of any stationary points and state weather it is a maximum, minimum or point of inflexion.

a) y=(2x-3)^6 For this one i've got the right co-ordinates but it's meant to be a mnimun point but i keep getting points of inflexion

b)y=x+(1/x)

c)y=((x+3)^4)-4x

d)y=(0.5x-1)^3

Help with any of these would really really be appreciated.
2. Have you tried differentiating it again and substituting in your x value into f"(x)?

If you have and it comes out as equal to zero, it doesn't necessarily make it a point of inflection I don't think :/
3. Yea did that and f"x = 0. i'll investigate a bit more and see what happens Thanks. Any idea about the others?
4. General method is:

1) Find derivative and set to 0 to find stationary point/max/min
So for a) it would be

implies

so is min/max/stationary point

Now need to find second order derivative:

and put in In this case that gives 0, so you gotta carry on with the differentiating. We see that we're gonna get zero until the 6th order derivative, i.e.

EDIT - made a mistake with the differentiating sorry!

This is a positive value, meaning the point must be a minimum.

For the others, is it the method or the differentiating you're having trouble with?
5. Okay thanks but i have no idea what this 6th order derivative thing is

For the others i'm not really sure.. i can't get started with b) cause i'm pretty sure if you defferentiate it d/dx=0 ?
6. Ok no worries about that 6th order derivative thing!

For b)

Writing it like this might make that more obvious

Is that a bit clearer?
7. Yea that helps a lot, thanks.
Whenever you equal that to zero then do you get x=1 and x=-1?
8. Whenever you equal that to zero then do you get x=1 and x=-1?
Yeah thats right, so you got two points to determine the nature of in this question!
9. Whoo Can you help with c) ? I keep getting the wrong co-ordinates?
I'm definately going to fail in life lol...
10. Man these are just all about practice - when I did my A levels I did like a million of them, then you screw up enough times to learn from the mistakes!

So c) y=((x+3)^4)-4x

Always remember that expressions can be split up when differentiating like this

So we get the result as

Giving

So

So

Putting this back into the original expression gives

11. Ahh okay. i understand. Thank you very much, you're a great help. Still not sure about a but i'll ask my teacher to explain 2moro

Turn on thread page Beta

### Related university courses

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: January 19, 2010
The home of Results and Clearing

### 3,078

people online now

### 1,567,000

students helped last year
Today on TSR

The latest news

### University open days

1. SAE Institute
Animation, Audio, Film, Games, Music, Business, Web Further education
Thu, 16 Aug '18
2. Bournemouth University
Clearing Open Day Undergraduate
Fri, 17 Aug '18
3. University of Bolton
Fri, 17 Aug '18
Poll
Useful resources

## Make your revision easier

### 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

Can you help? Study help unanswered threads

## Groups associated with this forum:

View associated groups

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE