You are Here: Home >< Maths

# Mistake? [FP1] watch

1. Surely there must be a mistake here in the mark scheme? [Part B]

I keep getting
Attached Images

2. (Original post by edothero)
Surely there must be a mistake here in the mark scheme? [Part B]

I keep getting
'Fraid not - markscheme is fine.

Point P has parameter p, and P' has parameter -p.

So, just replace p with -p throughout the equation for the normal at P, to get the equation for the normal at P'.

Note: Question says "write down", implying no calculcation is necessary.
3. (Original post by ghostwalker)
'Fraid not - markscheme is fine.

Point P has parameter p, and P' has parameter -p.

So, just replace p with -p throughout the equation for the normal at P, to get the equation for the normal at P'.

Note: Question says "write down", implying no calculcation is necessary.
This may sound stupid, but I'm trying to understand fully just in case a similar question pops up in the exam. How did you gather that P' has parameter -p and that P has parameter p? I don't think my brain is working properly today haha
4. (Original post by edothero)
This may sound stupid, but I'm trying to understand fully just in case a similar question pops up in the exam. How did you gather that P' has parameter -p and that P has parameter p? I don't think my brain is working properly today haha
By looking at the coordinates for P, P', and knowing the standard parameterisation for the parabola.
5. (Original post by edothero)
Surely there must be a mistake here in the mark scheme? [Part B]

I keep getting
Ah I was stuck on this question before, basically your gradient function should be in terms of y, so the gradient changes as well as the y co-ordinate

y^2 = 4ax
d(y^2=4ax)/dx = 2y(dy/dx)=4a so dy/dx = 4a/2y
6. For part b your finding the equation of the normal for p' not just p. Thats why the answer in the mark scheme is correct. I think you may have confused p and p'

Posted from TSR Mobile

### 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: May 10, 2015
Today on TSR

### Edexcel C4 Maths Unofficial Markscheme

Find out how you've done here

### 1,069

students online now

Exam discussions

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