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

# Differentiation - Stationary Points watch

1. The stationary points of the equation:

y = 2x^3 + 7/2 x^2 - 3x +1

The x values are 1/3 and -3/2, that gives y values of 25/54 and 53/8 respectively.

The text book has the y value when x=1/3 as -25/54.

What am I doing wrong as no matter what I do I can't get a negative when x=1/3?

Or is there a typo in the answers given and it should be +25/54?
2. (Original post by gerrya271)
The stationary points of the equation:

y = 2x^3 + 7/2 x^2 - 3x +1

The x values are 1/3 and -3/2, that gives y values of 25/58 and 53/8 respectively.

The text book has the y value when x=1/3 as -25/58.

What am I doing wrong as no matter what I do I can't get a negative when x=1/3?

Or is there a typo in the answers given and it should be +25/58?
Typo, though it should be 54 not 58 on the denom.
3. (Original post by RDKGames)
Typo, though it should be 54 not 58 on the denom.
Yeah sorry, I have 54 on the bottom not 58.

So it's deffo positive and therefore a typo in the answers in the book?
4. (Original post by gerrya271)
Yeah sorry, I have 54 on the bottom not 58.

So it's deffo positive and therefore a typo in the answers in the book?
Yes. Graph it yourself on some software if you need convincing.
5. (Original post by RDKGames)
Yes. Graph it yourself on some software if you need convincing.
I just wanted to double check as I tutor my daughters and her friends for Maths and it simply didn't seem possible to get a negative answer when x=1/3, but it's always a bit off putting when the answers in the back of the book say otherwise.

Thank you for confirming that I've not suddenly lost my ability to count!!

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: October 12, 2017
Today on TSR

### Exam Jam 2018

All day biology and life sciences revision thread

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