You are Here: Home >< Maths

# Difference between f(-x) and f(|x|)?? (C3) watch

1. If I know the graph for f(x), would the graph for f(-x) and f(|x|) be the same, i.e. a reflection in the y axis?

Thanks
2. f(|x|) is only changed left of the y-axis -- the graph for the values of x that are already positive remains unchanged. Hope this helps.
3. (Original post by jbuck100)
If I know the graph for f(x), would the graph for f(-x) and f(|x|) be the same, i.e. a reflection in the y axis?

Thanks
I don't think they would be the same. The modulus of a graph isnt a reflection in the y axis (or x axis), it's just the absolute value of the number (i.e. positive).

Consider y=x

If you had f(-x), then X>0 would become negative and X<0 would become positive.

If you had f(|x|), then just X<0 would change to become positive, becoming a V shape with the origin being the point of intersection with the x axis.
4. nah, f(-x) is a reflection in the y axis - you flip it all over, whereas f(|x|) is everything on the right of the y axis reflected onto the left, and you 'delete' what would usually be on the left. if that makes sense
5. No, think about where you would plot certain values - such as x=-1. Do they do in the same place?
6. f(-x) is a reflection in the y axis

f(|x|) is a reflection in the y axis except that it's just the bit on the right "pasting" itself on to the left of the y axis. if you think about it, it's because f(-1) ends up being the same as f(1), f(-4) = f(4) etc so the y values are the same as on the positive side of the y axis

edit; ok that got answered 5 times quickly
7. good point i think they are the same
8. Aah thank you that's made it so much clearer!

(Original post by victor_b1992)
good point i think they are the same
..lol
9. but it kinda is
10. f(-x) is / changed to \
f(lxl) is / change to V

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 14, 2010
Today on TSR

### Are you living on a tight budget at uni?

From budgets to cutbacks...

### University open days

1. Loughborough University
Fri, 21 Sep '18
2. University of Cambridge
Fri, 21 Sep '18
3. Richmond, The American International University in London
Fri, 21 Sep '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