Main content

## Algebra 1

### Unit 10: Lesson 1

Graphs of absolute value functions- Shifting absolute value graphs
- Shift absolute value graphs
- Scaling & reflecting absolute value functions: equation
- Scaling & reflecting absolute value functions: graph
- Scale & reflect absolute value graphs
- Graphing absolute value functions
- Graph absolute value functions
- Absolute value graphs review

© 2023 Khan AcademyTerms of usePrivacy PolicyCookie Notice

# Scaling & reflecting absolute value functions: equation

CCSS.Math:

The graph of y=k|x| is the graph of y=|x| scaled by a factor of |k|. If k<0, it's also reflected (or "flipped") across the x-axis. In this worked example, we find the equation of an absolute value function from a description of the transformation performed on y=|x|.

## Want to join the conversation?

- Is there any way to tilt or rotate the function? I.e rotate the function by say 45 degrees.(7 votes)
- yes, there is a way, but it requires knowledge of things called parametric equations, trigonometry, and also linear algebra. you'll encounter these later on in your math classes (assuming you take them past grade 10)(7 votes)

- The 7 is the slope, right?(5 votes)
- Sort of, but not quite. The function would be f(x) = - 7 | x|. For x ≤ 0, the slope would be 7 with a y intercept of (0,0). For x ≥ 0, the slope would be -7 with a y intercept of (0,0). So you have to consider which part of the graph you are talking about.(10 votes)

- what scaled even mean?(4 votes)
- "Scaled" means the graph rises faster or slower than the standard function of y=|x|. For example, y=2|x| rises twice as fast so the V-shape will be narrower.

Hope this helps.(5 votes)

- Can u flip it on the y axis as well?(3 votes)
- Yes you can flip it on y axis if the points are on the left or right side of the axis.(3 votes)

- What if we scaled horizontally by a factor of 7?(2 votes)
- Scaling horizontally by a factor of 7 means that instead of 𝑥 we get 7𝑥.

So, scaling 𝑦 = −|𝑥| horizontally gives us 𝑦 = −|7𝑥|.(2 votes)

- So scaling by a factor of 7 is different from just moving the function up by 7 like in the previous video?(2 votes)
- Yes. Scaling is sort of like stretching the graph vertically, where as moving the function up preserves the shape. If the function is x, scaling it would produce 7x, where as moving it upwards produces x+7. If you graph both functions, you can clearly see the difference.(1 vote)

- In the previous video, we added 7 to the equation. Now we're
*multiplying*. by 7. Why don't we just add 7 like the other video?(2 votes)- When we graphed linear equations, we saw that y = x+7 is not the same as y = 7x.

y = 7x means for every x, y is 7 times as large. This produces a very steep line.

The same thing applies here. "Scaled vertically" is a fancy way of saying the line looks steeper (i.e. stretched along the y-axis). y = 7|x| means for every x, y is 7 times as large.

On the other hand, y = |x| + 7 means you add seven to each x to get y.(1 vote)

- Why do we call it "vertical" scaling? What's the difference between scaling such graphs vertically and horizontally?(2 votes)
- sal says, "hopefully this is familiar. You've seen the graph of y is equal to absolute value of x before."

I have not. This is not familiar. Would someone please provide a link to where I need to go on Khan? Thank you!(1 vote)- You can always search a topic next to the courses on top. THis leads to https://www.khanacademy.org/math/arithmetic/arith-review-negative-numbers/arith-review-abs-value/a/intro-to-absolute-value

The issue is that videos are being moved around to different levels just as they are in schools.(3 votes)

- Confused. Since x is absolute value it is always positive? How can the graph go to the left of zero?(1 vote)
- The value of "x" doesn't need to be positive. The absolute value turns "x" into a positive. For example, if x=-3, then |-3|=+3. The absolute value is impacting the value of Y, not X.

Hope this helps.(2 votes)

## Video transcript

- [Instructor] The graph of y is equal to absolute value of x is reflected across the x-axis and then scaled vertically
by a factor of seven. What is the equation of the new graph? So pause the video and see
if you can figure that out. Alright, let's work
through it together now. Now, you might not need
to draw it visually but I will just so that
we can all together visualize what is going on. So let's say that's my x-axis and that is my y-axis. y equals the absolute value of x. So for non-negative values of x, y is going to be equal to x. Absolute value of zero is zero. Absolute value of one is one. Absolute value of two is two. So it's gonna look like this. It's gonna have a slope of one and then for negative values, when you take the absolute value, you're gonna take the opposite. You're gonna get the positive. So it's gonna look like this. Let me see if I can draw
that a little bit cleaner. This is a hand drawn
sketch so bear with me but hopefully this is familiar. You've seen the graph of y is equal to absolute
value of x before. Now, let's think about the
different transformations. So first, they say is
reflected across the x-axis. So for example, if I have some x value right over here, before, I would take
the absolute value of x and I would end up there but now we wanna reflect across the x-axis so we wanna essentially get
the negative of that value associated with that corresponding x and so for example, this x, before, we would get
the absolute value of x but now we wanna flip across the x-axis and we wanna get the negative of it. So in general, what we are doing is we are getting the negative
of the absolute value of x. In general, if you're
flipping over the x-axis, you're getting the negative. You're scaling the expression
or the function by a negative. So this is going to be y
is equal to the negative of the absolute value of x. Once again, whatever absolute value of x was giving you before for given x, we now wanna get the negative of it. We now wanna get the negative of it. So that's what reflecting
across the x-axis does for us but then they say scaled
vertically by a factor of seven and the way I view that is if
you're scaling it vertically by a factor of seven, whatever y value you got for given x, you now wanna get seven times the y value, seven times the y value for a given x. And so if you think
about that algebraically, well, if I want seven times the y value, I'd have to multiply this thing by seven. So I would get y is
equal to negative seven times the absolute value of x and that's essentially
what they're asking, what is the equation of the new graph, and so that's what it would be. The negative flips us over the x-axis and then the seven scales
vertically by a factor of seven but just to understand
what this would look like, well, you multiply zero times seven, it doesn't change anything but whatever x this is, this was equal to negative x but now we're gonna get
to negative seven x. So let's see, two, three,
four, five, six, seven so it'd put it something around that. So our graph is now going to look, is now going to look like this. It's going to be stretched
along the vertical axis. If we were scaling vertically by something that had an
absolute value less than one then it would make the graph less tall. It would make it look, it would make it look wider. Let me make it at least look
a little bit more symmetric. So it's gonna look something, something like that but the key issue and the reason why I'm
drawing is so you can see that it looks like it's
being scaled vertically. It's being stretched in
the vertical direction by a factor of seven and the
way we do that algebraically is we multiply by seven and the negative here is what
flipped us over the x-axis.