You are Here: Home >< Maths

# HELP!! f(x) maths question watch

1. So I’ve got a question where f(x) = (x - 1) (x + 2) and I have to draw the graph y = f(x + 2). I’ve got the x axis intersections as -4 and -1, however I don’t understand how the y axis intersection is 4... I mean if x is 0, y = -1 x 2 = -2; and then add 2 makes 0? Not 4? Please help where I’ve went wrong!
2. if x =0 then y=f(2) f(2) =?
3. If x=0, f(x+2) = f(0+2) = f(2)

(2-1)(2+2) = 4
4. (Original post by funkybinoculars)
So I’ve got a question where f(x) = (x - 1) (x + 2) and I have to draw the graph y = f(x + 2). I’ve got the x axis intersections as -4 and -1, however I don’t understand how the y axis intersection is 4... I mean if x is 0, y = -1 x 2 = -2; and then add 2 makes 0? Not 4? Please help where I’ve went wrong!
graph moves two steps to the left-the y-intercept should be 4 now. if not then im not sure
5. Be careful for the difference between "f(x+a)" and "f(x) + a"!
(Where "a" is a constant).

For x-y graph transformations:

- f(x-a),
Shifts f(x) by a-units on the X-AXIS to the right
(Therefore negative values of "a" shift f(x) by "|a|"-units to the left on the x-axis).

We can see this by your example, f(x) = (x-1)(x+2), there are x-intercepts at x=1 and x=-2.
Therefore f(x+2) = (x+1)(x+4), has x-intercepts at x=-1 and x = -4, (shifted by -2 units on x-axis).
-----------------------------------------------------------------------------------------------------------------------------

-f(x) + a,
Shifts f(x) up by "a" units on the Y-AXIS
(Similarly, if "a" is a negative value, the f(x) is shifted DOWN by "|a|" units on the y-axis).

For your example, f(x) = (x-1)(x+2), has y-intercept at y = (-1)(2) = -2.
f(x) + 2 = (x-1)(x+2) + 2, has y-intercept y= (-1)(2) + 2 = 0.
6. (Original post by funkybinoculars)
So I’ve got a question where f(x) = (x - 1) (x + 2) and I have to draw the graph y = f(x + 2). I’ve got the x axis intersections as -4 and -1, however I don’t understand how the y axis intersection is 4... I mean if x is 0, y = -1 x 2 = -2; and then add 2 makes 0? Not 4? Please help where I’ve went wrong!

f(x) = (x - 1)(x + 2) becomes f(x + 2)

This means that every value of x in the orignal equation becomes 'x + 2'.

Your problem was that you were substituting x = 0 into f(x) and not f(x+2)

### 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: October 15, 2017
Today on TSR

### Edexcel GCSE Maths Unofficial Markscheme

Find out how you've done here

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