You are Here: Home >< Maths

# OCR A2 maths january, C3/C4/S2 question. watch

1. (Original post by 01234567)
c3 Jan 2010.

f(x) = 2 − (√3x + 1)^1/3
Find the set of values of x for which f(x) = |f(x)|.

I equated fx to itself and to -fx.. Is this the right way to do the question?
Not really

The mark scheme has the answer down as x is less or equal to 7.
You have to consider the point at which f(x) = 0

when f(x)>0, |f(x)| does not change so |f(x)|= f(x)

if f(x)<0, then |f(x)|=-f(x) which is no good to you
2. (Original post by 01234567)

5)ii) Find an expression for the second derivative and hence ﬁnd the value of
the second derivative at the stationary point.
I got the right answer up to a point in the mark scheme.
To find out the second derivative at the stationary point is this the same as just equating dy/dx = 0?
From the mark scheme, they appear to have substituted x = 0 to find out the stationary point from the equation... so, is this different for the second derivative?
Difficult to comment without the question
3. (Original post by TenOfThem)
Difficult to comment without the question
4. so, in part (i) you showed that x=0 at the stationary point

That is why you use x=0

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 5, 2013
Today on TSR

### Cambridge interviews

Find out which colleges are sending invitations

### University open days

• University of East Anglia
Fri, 23 Nov '18
• Norwich University of the Arts
Fri, 23 Nov '18
• Edge Hill University
Sat, 24 Nov '18
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