Shift, flip and stretch

Graph transformations, visually

Every move changes the rule in one place. A change outside the brackets acts on heights. A change inside acts on x, and acts backwards. Drag the sliders and watch the gray parent shape turn into the blue one.

Free to start. Coming soon to the App Store.

y = 1(x − 2)² + 1
  1. (x − 2): 2 to the right
  2. + 1: up 1
  3. 1 in front: no flip, no stretch
Moved 2 to the right and 1 up. Pip stands on the new bottom, at (2, 1).
Idea 1 · Lift or lower

Lift or lower: add at the end

Add a number at the end of the rule and every height goes up by that number: y = x² + 2 is the parabola x² lifted by 2. A negative number lowers it.

Nothing else changes. The shape, the width and the left-right position stay exactly as they were. This is a vertical shift.

Aha!

Changes outside the brackets act on heights: add 2 and every point goes up 2.

Idea 2 · Slide sideways

Slide sideways: it goes the other way

Change the inside and the shape slides sideways, and it goes backwards: y = (x − 3)² moves 3 to the right, not left.

The bottom of the bowl is where the inside equals zero. For (x − 3) that happens at x = 3. Moving the wrong way is the most common slip with the sign of h.

Aha!

Changes inside act on x, and act backwards: (x − 3) slides the shape 3 to the right.

Idea 3 · Flip with a minus

Flip with a minus

A minus in front flips the shape upside down: y = −√x. A minus on x flips it left to right: y = √(−x).

On x² you cannot see the second flip, because x² is already symmetric. The square root has only one side, so it shows both flips clearly.

Aha!

A minus in front flips the heights. A minus on x flips left and right.

Idea 4 · Stretch and squash

Stretch and squash

A number in front pulls the shape taller (bigger than 1) or flatter (between 0 and 1): y = 2x² looks narrower, not wider.

A number on x acts sideways and backwards: y = (2x)² squeezes the shape toward the y-axis. Telling the two apart, and doing several moves in the right order, is the skill.

Aha!

A number in front pulls the shape taller or flatter. A number on x acts sideways, and backwards.

Quick answers

Questions about transformations

Why does (x − 3) move the graph to the right?

The bowl reaches its bottom when the inside equals zero. For (x − 3)² that happens at x = 3, so the whole graph shifts 3 to the right. Changes inside the brackets always act backwards.

What is the difference between a vertical and a horizontal shift?

A vertical shift adds a number outside the function, like f(x) + 2, and moves the graph up. A horizontal shift changes the input, like f(x − 2), and moves it right. Outside changes act on heights, inside changes act on x.

How do you reflect a graph over the x-axis or the y-axis?

Put a minus in front, −f(x), to flip it over the x-axis. Put a minus on x, f(−x), to flip it over the y-axis.

In which order do you apply several transformations?

In the same order you would calculate the rule: the inside first, then the multiplier, then the number added at the end. For y = −2(x − 1)² + 3: shift right 1, stretch by 2 and flip, then shift up 3.

Now play it

Try it in Pip: Math Adventure

World 4 of Pip: Math Adventure is about transformations. You slide, flip and stretch a shape so Pip lands on the gems, and you read the moves from the equation.

It is a math game for iPhone, coming soon to the App Store. Join the list and we will tell you the day Pip is out.