Describe and sketch how a graph moves or flips when f(x) becomes f(x) + a, f(x + a), −f(x) or f(−x). It is Higher only, aimed at grade 8. Free questions with answers are on this page. Worked examples show each line before you try the questions.
y=f(x)+a is a vertical shift. y=f(x+a) is a horizontal shift the opposite way (left if a>0). y=−f(x) reflects in the x-axis. y=f(−x) reflects in the y-axis. y=af(x) stretches in y; y=f(ax) stretches in x by factor a1. Apply one at a time if two transformations sit together, and watch the order.
A point (2,5) on y=f(x) becomes (2,8) on y=f(x)+3 and (−2,5) on y=f(−x). Sketch the parent faintly, then the image boldly. Name the transformation in full: 'translation by (03)', not just 'up'.
Outside the function moves y: f(x)+a is up, −f(x) is a reflection in x-axis. Inside moves x, and the x-shift is the opposite of the sign: f(x+2) is 2 left. f(−x) reflects in the y-axis. Apply one transformation at a time to a known point.
Objectives
Move a graph left or right from inside the bracket.
Reflect a graph with -f(x) or f(-x).
Track a point, not only the whole curve.
Key points
Recognise the four transformations from the algebra: f(x)+a, f(x+a), −f(x) and f(−x).
Move a single point (such as a turning point or intercept) under each transformation.
Sketch the transformed graph on the same axes as the original, keeping its shape.
Describe a transformation in words: 'translation by (a0)' or 'reflection in the x-axis'.
Worked examples
Example 1
State the direction of the translation y=f(x+4).
2 marks
The 4 is inside the bracket
Inside a plus sign moves the graph left
Left
Answer: left
Common slips
Slip: The 4 is added to y Inside affects x, not the height.
Slip: Plus means right The slide is opposite to the sign inside.
Slip: Right Right would be f(x-4).
Example 2
The point (3, 2) is on y=f(x). Give its image on y=f(x+1).
2 marks
f(x+1) moves the graph left by 1
The x-coordinate decreases by 1
(2, 2)
Answer: (2, 2)
Common slips
Slip: It moves the graph up by 1 The change is inside the bracket.
Slip: The x-coordinate increases Left means a smaller x.
Slip: (4, 2) y is unchanged because nothing was added outside.
Example 3
The point (8, 1) is on y=f(x). Where is it on y=f(-x)?
3 marks
f(-x) is a reflection in the y-axis
Change the sign of the x-coordinate
(-8, 1)
Answer: (-8, 1)
Common slips
Slip: It is a reflection in the x-axis The minus is inside the bracket, so it changes x, not y.
Slip: Change the sign of y The height of the point does not change.
Slip: (8, -1) (8, -1) is the image on y=-f(x).
Questions and answers
GCSE Maths transforming graphs y = f(x) questions and answers. Try each one, then open the answer. Easy questions come first.
Question 1 Easy2 marks
In which direction does y=f(x+2) move the graph?
Show answer
Answer: left
Plus inside the function moves the opposite way.
The slide is horizontal.
M1 — Plus inside the function moves the opposite way.
A1 — Answer left
Question 2 Easy2 marks
In which direction does y=f(x-3) move the graph?
Show answer
Answer: right
Minus inside moves the graph the other way from f(x+3).
The distance is 3.
M1 — Minus inside moves the graph the other way from f(x+3).
A1 — Answer right
Question 3 Medium2 marks
(3, 2) lies on y=f(x). Write its image on y=-f(x).
Show answer
Answer: (3, -2)
-f(x) reflects in the x-axis.
Change the sign of y and keep x.
M1 — -f(x) reflects in the x-axis.
A1 — Answer (3, -2)
Question 4 Medium2 marks
y=-f(x) reflects the graph in which axis?
Show answer
Answer: x-axis
Every y-coordinate changes sign.
The mirror line is horizontal.
M1 — Every y-coordinate changes sign.
A1 — Answer x-axis
Question 5 Hard2 marks
Describe the translation y=f(x+2)+3 as a horizontal word, a number, then the vertical word and number.
Show answer
Answer: left 2 then up 3
Inside +2 is a move left.
Outside +3 is a move up.
M1 — Inside +2 is a move left.
A1 — Answer left 2 then up 3
Question 6 Hard2 marks
(6, 4) lies on y=f(x). Give its image on y=f(-x).
Show answer
Answer: (-6, 4)
f(-x) reflects in the y-axis.
Change the sign of x and leave y as 4.
M1 — f(-x) reflects in the y-axis.
A1 — Answer (-6, 4)
Question 7 Exam-style4 marks
The curve y=f(x) has a turning point at (4, 5). Describe fully the two transformations that map y=f(x) to y=-f(x)+1, and find the turning point of y=-f(x)+1.
Show answer
Answer: (4, -4)
-f(x) is a reflection in the x-axis, so (4, 5) goes to (4, -5).
The +1 outside is a translation by the vector (0, 1).
So -5 goes up to -4.
Turning point (4, -4).
B1 — Reflection in the x-axis
B1 — Translation by the vector (0, 1)
M1 — (4, -5) or y-coordinate -5 then add 1
A1 — (4, -4)
Common mistakes
Most lost marks on this topic are one slip.
Saying f(x+2) moves the graph right
A plus inside the bracket moves the graph left
Mixing up -f(x) and f(-x)
A minus outside flips y, a reflection in the x-axis. A minus inside flips x, a reflection in the y-axis
Changing x for f(x)+a
A number outside the bracket only changes the y-coordinate
Spot the slip
Sam says y=f(x+2) moves the graph right. Which way does it move?
Left
Right
Up
Show the slip
Left Adding inside the bracket moves the graph the other way. f(x+2) moves left.
Exam tips
Be ready to do this without a calculator. Paper 1 is the non-calculator paper.
If the question says “show that”, the result is given. The marks are for the steps that reach it.
The method is the same on AQA-style and Edexcel-style papers.
Before sketching, write the transformed coordinates of the turning point and the intercepts — those labelled points are where the marks are.
For f(x+a), a quick check: the new graph must equal the old one when the inside is the same, so the point where x+a=0 is the old x=0 point.
Printable worksheet
The same questions are in a PDF you can print. Answers start on a later page.