You are Here: Home >< A-levels

# Exponential Growth/Decay - Core 4 January 2013 AQA Watch

1. Question 7 bii) on this paper here: http://filestore.aqa.org.uk/subjects...4-QP-JAN13.PDF

I'm unsure as to why when you want to find the maximum rate of growth you don't but dN/dt = 0 and factorise it to find the stationary values of N, and substitute them back into the original equation. I know this is wrong because you end up with an e^-t/8 = 0, but I don't understand why.

However according to the mark scheme you find the second differential and put that = 0 to find the value of N at which the maximum rate of growth occurs, could somebody please explain why this is the case?

Thanks for any help anyone can give
2. (Original post by danbroown)
Question 7 bii) on this paper here: http://filestore.aqa.org.uk/subjects...4-QP-JAN13.PDF

I'm unsure as to why when you want to find the maximum rate of growth you don't but dN/dt = 0 and factorise it to find the stationary values of N, and substitute them back into the original equation. I know this is wrong because you end up with an e^-t/8 = 0, but I don't understand why.

However according to the mark scheme you find the second differential and put that = 0 to find the value of N at which the maximum rate of growth occurs, could somebody please explain why this is the case?

Thanks for any help anyone can give
The keyword is 'maximum' in 'maximum rate of change'. The rate of change can take a range of values, given by dN/dt, but the maximum will be where the rate of change of the rate of change (the second differential) is equal to 0.
3. (Original post by SeanFM)
The keyword is 'maximum' in 'maximum rate of change'. The rate of change can take a range of values, given by dN/dt, but the maximum will be where the rate of change of the rate of change (the second differential) is equal to 0.
Thank you, that helps

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: June 16, 2016
Today on TSR

### Last-minute PS help

100s of personal statements examples here

### More pressure for kinky sex?

Discussions on TSR

• Latest
• ## See more of what you like on The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

• Poll

## All the essentials

### Student life: what to expect

What it's really like going to uni

### Essay expert

Learn to write like a pro with our ultimate essay guide.

### Create a study plan

Get your head around what you need to do and when with the study planner tool.

### Resources by subject

Everything from mind maps to class notes.

### Study tips from A* students

Students who got top grades in their A-levels share their secrets

## Groups associated with this forum:

View associated groups
Discussions on TSR

• Latest
• ## See more of what you like on The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

• 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

Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.