Maths (A2 question)

A curve has the equation y=2(x-1)/x^2 +3 and crosses the x-axis at point A.
a) show that the normal to the curve at A has the equation y=2-2x

Reply 1

Kevin De Bruyne

Original post by SpongyMesophyll

A curve has the equation y=2(x-1)/x^2 +3 and crosses the x-axis at point A.
a) show that the normal to the curve at A has the equation y=2-2x

What have you tried so far? :h:

Reply 2

SpongyMesophyll

Original post by SeanFM

What have you tried so far? :h:

I've tried using the quotient rule, where I get to (-2x^2 +4+6)/(x^2 +3)^2
I don't know where to go from there, or even if I'm right

Reply 3

Kevin De Bruyne

Original post by SpongyMesophyll

I've tried using the quotient rule, where I get to (-2x^2 +4+6)/(x^2 +3)^2
I don't know where to go from there, or even if I'm right

Edit: I think you mean 4x there, unfortunate typo :tongue:

After that, think about what you've actualy found using the quotient rule and what is required/given in the question.

(edited 7 years ago)

Reply 4

SpongyMesophyll

sorry i meant to put 4x instead of 4. I don't know how to get to 2x or how to simplify from there. sorry xD

Reply 5

Kevin De Bruyne

Original post by SpongyMesophyll

sorry i meant to put 4x instead of 4. I don't know how to get to 2x or how to simplify from there. sorry xD

Apologies, you are right - it is 4x.

So what have you actually calculated using the quotient rule, and how will it be useful to the question?

What parts of the question can you now do stuff with?

Reply 6

SpongyMesophyll

I believe that I have found the gradient. apart from that I am lost

Reply 7

Kevin De Bruyne

Original post by SpongyMesophyll

I believe that I have found the gradient. apart from that I am lost

Please quote me so I know you have replied :h:

Correct, you've found f'(x), a function to find the gradient at a given point x.

The question talks about a point A, gives you some information about it and asks you to find something about it. How can you do those things? The function you've found plays a part and I think you will know how to use it when you need it. Becauae you've differentiated f (x) for some reason which is right, which leads me to suspect that you know you need to use it for something.

(edited 7 years ago)

Reply 8

SpongyMesophyll

Original post by SeanFM

Please quote me so I know you have replied :h:

I only integrated because that was the topic in which the question was in. I really am lost xD.

Reply 9

Zacken

Original post by SpongyMesophyll

I only integrated because that was the topic in which the question was in. I really am lost xD.

What's the point A? As in, what are it's coordinates?

Reply 10

Kevin De Bruyne

Original post by SpongyMesophyll

I only integrated because that was the topic in which the question was in. I really am lost xD.

Think about the questiom asked above. The natural step is to find A first and then you may see how to use it.

Reply 11

SpongyMesophyll

Original post by SeanFM

Think about the questiom asked above. The natural step is to find A first and then you may see how to use it.

I got that y=-2/3 when x=0. help XD

Reply 12

Kevin De Bruyne

Original post by SpongyMesophyll

I got that y=-2/3 when x=0. help XD

Before I check it, is that good or bad.. reassuring.. puzzling?

Reply 13

SpongyMesophyll

Original post by SeanFM

Before I check it, is that good or bad.. reassuring.. puzzling?

I think it may be right. I'm just so lost and don't know what to do

Reply 14

Kevin De Bruyne

Original post by SpongyMesophyll

I think it may be right. I'm just so lost and don't know what to do

Okay, let's assume it's right. The question asks you to find the normal to the curve at A.. you've found the point A. How do you find the equation of the normal to the curve at that point?

If it helps, past this point (given your previous working) it is no longer C3 knowledge but something you have covered in AS Maths.