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

# Making y the subject of an equation watch

1. In an implicit differentiation question (This is the 4th equation I'm doing these steps for but all have been just 3 terms, not 5), it asks:

for the equation x^2 + y^2 - 2x - 4y - 4 = 0;

i) find dy/dx by implicit differentiation
Which I have done, and found dy/dx = (1-x)/(y-2).

ii) by solving the equation for y, find the two functions defined by the equation.
I'm struggling with this one, I've got as far as y^2 - 4y = - x^2 + 2x + 4 and can't work out how to get any further with this.

The next two parts I think are doable once I know how to do ii.
iii) find the derivative of each of the functions found in ii)
iv) verify the results obtained in i) and iii) are in agreement

2. (Original post by ThatTallGuy)
In an implicit differentiation question (This is the 4th equation I'm doing these steps for but all have been just 3 terms, not 5), it asks:

for the equation x^2 + y^2 - 2x - 4y - 4 = 0;

i) find dy/dx by implicit differentiation
Which I have done, and found dy/dx = (1-x)/(y-2).

ii) by solving the equation for y, find the two functions defined by the equation.
I'm struggling with this one, I've got as far as y^2 - 4y = - x^2 + 2x + 4 and can't work out how to get any further with this.

The next two parts I think are doable once I know how to do ii.
iii) find the derivative of each of the functions found in ii)
iv) verify the results obtained in i) and iii) are in agreement

You have an equation of the form

where .

How can you solve an equation of this form?

EDIT: Actually, it's probably quicker to write it as and then factorise the left-hand-side.
3. Ah I didn't think about doing that, thank you! That made it much more simple!

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 27, 2015
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