You are Here: Home >< A-levels

# Differentiate y = ln(x^2 + 9)^-1 using chain rule: y=lnu u=(x^2 + 9)^-1 dont work?! Watch

1. Differentiate y = ln(x^2 + 9)^-1 using chain rule: y=lnu u=(x^2 + 9)^-1 dont work?!

I have the correct solution but I want to solve this way.

But my du/dx= -2x * (x^+9)^-2 whhich looks wrong.
2. (Original post by girlwonder17)
Differentiate y = ln(x^2 + 9)^-1 using chain rule: y=lnu u=(x^2 + 9)^-1 dont work?!

I have the correct solution but I want to solve this way.

But my du/dx= -2x * (x^+9)^-2 whhich looks wrong.
let ln(x^2 + 9)^-1= -ln(x^2 + 9) then use the chain rule
3. (Original post by meowgoesthedog)
let ln(x^2 + 9)^-1= -ln(x^2 + 9) then use the chain rule
thanks but i have solved with this method

also

with ln1 - ln(x^2 +9)

but how can I solve with the chain rule with the y and u as I mentioned pls?
4. (Original post by girlwonder17)
thanks but i have solved with this method

also

with ln1 - ln(x^2 +9)

but how can I solve with the chain rule with the y and u as I mentioned pls?
You forgot the dy/du part for the chain rule above; (dy/du)*(du/dx)=(dy/dx)
Your du/dx is correct, just multiply it by dy/du and cancel and you should get the same answer
5. (Original post by Poooky)
You forgot the dy/du part for the chain rule above; (dy/du)*(du/dx)=(dy/dx)
Your du/dx is correct, just multiply it by dy/du and cancel and you should get the same answer
omg blonde moment solved it now

tysm <3

Updated: October 12, 2016
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:
Today on TSR

### Summer on a budget

How do you have a great summer on the cheap?

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