Cubic Transformations - Graph shown is best represented by the equation:

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Discussion Overview

The discussion revolves around understanding horizontal transformations of cubic functions, specifically how to interpret graphs represented by equations of the form f(x+a) and f(x-a). Participants explore the implications of these transformations on the graph's position and shape.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants express confusion regarding the interpretation of horizontal transformations and how they affect the graph's position along the x-axis.
  • One participant suggests a rule of thumb for determining the direction of horizontal translations, stating that f(x+a) moves the graph a units to the left and f(x-a) moves it a units to the right.
  • Another participant proposes that the equation f(x)=-(x-a)^3 +b is a potential representation of the graph, but questions arise about its validity.
  • Concerns are raised about the implications of comparing different cubic functions, particularly regarding the direction of the graph and the effects of transformations.
  • One participant notes that when x=a, y=b, which leads to the elimination of certain options based on the behavior of the cubic function.
  • A question is posed about the implications of using (-a,b) instead of (a,b) in the context of the transformations discussed.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the correct interpretation of the transformations or the validity of the proposed equations. Multiple competing views and interpretations remain present throughout the discussion.

Contextual Notes

Participants rely on specific assumptions about the behavior of cubic functions and their transformations, but these assumptions are not universally agreed upon. The discussion also highlights the complexity of interpreting graphical representations of mathematical functions.

confusedatmath
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I am confused about using horizontal transformations such as

f(x+a) and f(x-a) to interpret these graphs.
 

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confusedatmath said:
<snip>

I am confused about using horizontal transformations such as

f(x+a) and f(x-a) to interpret these graphs.

A rule of thumb I use to work out horizontal translations is that the graph moves along the x-axis in the opposite direction to the sign in the function. That is $$f(x+a)$$ moves $$a$$ units to the left (-ve) and $$f(x-a)$$ moves $$a$$ units to the right (+ve).

You can verify the direction by plugging values in and seeing what happens. Your example is a cubic so suppose we have the "base" function $$f(x) = x^3$$. It is pretty clear that $$f(x) = 0 \text{ when } x = 0$$. Now suppose we have $$f(x-4)$$ (where a=4). This translation is shifted 4 units to the right according to the previous paragraph and $$f(x-4) = 0 \text{ when } x-4 = 0 \therefore x=4$$ which is 4 units to the right of 0.

Let me know if you meant something elseedit: If I take your first example the point (a,b) is to the left of 0 on the x-axis so it'll be which sign inside the function
+. Giving us (x+a)^3
 
But the answer is f(x)=-(x-a)^3 +b ...
 
confusedatmath said:
But the answer is f(x)=-(x-a)^3 +b ...

That doesn't make sense to me. I tried it with a graph in wolfram showing the graphs of $$f(x) = -(x+5)^2 \text{ with } g(x) = -x^3$$ for comparison and the graph of f(x) is shifted 5 units left compared to g(x).
 
The first thing you should notice is that when x= a, y= b. Since all of the options have "+ b", the cubic portion must be 0 when x= a so those that have "x+ a" are impossible. That eliminates D and E.

The second thing you should notice is that the usual x^3 is reversed- this graph rises to the left, not the right. That means x is swapped for -x. Since we are using "x- a" instead of x, we must have -(x- a)^3 which is the same as (a- x)^3. That eliminates A leaving B and C which are identical.
 
Last edited by a moderator:
so we sub x=a because in the graph it says (a,b)

what if the question said (-a,b) ??
 

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