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With the image below I try to explain in which way substituting (x-a) ( with a> 0) for x in the expression defining a function results in a shift to the right, although " intuition" tells us it should result in a shift to the left. To do this I use the auxiliary idea of "shifting" as "copying" or "imitating".

I would be interested in knowing whether this explanation could be efficient in the classroom at the high school level.

Suppose we have $y=f(x)=x^2$ and want to graph $y=g(x)=f(x-1).$

The function $g$ maps each $x$ to the image of $(x-1)$ under the function $f$.

In other words, each $x$ value has an "$ x-1$ " ( his own "$x-1$" ) , and copies his (x-1) 's image under the "old" mapping $f$ .

Since each "imitator" ( each $x$ value) is to the RIGHT of it's "model", that is it's " $x-1 $" , the change from the function $f(x)=x^2$ to the function $ g(x)=f(x-1)$ results , for each "old" point of the graph of f, in a translation of $1$ unit to the RIGHT.

enter image description here

Remark. - I first used the idea of " stealing" , for which I substitute the idea of " copying" or "imitating". I've just seen a post of Hyperpallium using the idea of " sampling" , even better.

Link to Hyperpallium's post : *Seeing* why horizontal shifts are reversed?

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    $\begingroup$ This link is a good post explaining this concept, because at the moment your explanation is overcomplicating the situation quite alot $\endgroup$ – Hushus46 Mar 25 at 21:46
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    $\begingroup$ I'm voting to close this question as off-topic because it is about teaching mathematics (Math Educators SE) and not based on an understand, or lack thereof, of various mathematical fields. $\endgroup$ – Chase Ryan Taylor Mar 25 at 21:50
  • $\begingroup$ @ Hushus46 . Thanks for the link. $\endgroup$ – Ray LittleRock Mar 25 at 21:53
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Yes it moves the whole plane by 1 in x dimension. I would like to call it swiping instead of stealing. Nothing is taken, it's just shuffled around a bit.

Imagine swiping a whole image on a mobile phone screen 1 step right but none in up-down direction.

It is a good insight. First step towards geometric transformations, rotations, projections.

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Your suggestion is nothing deeper than this:

enter image description here

Ignore all the confusing suggestions about "stealing." Certainly not helpful. Certainly not beautiful.

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  • $\begingroup$ This drawing is self explanatory. Thanks! $\endgroup$ – Ray LittleRock Mar 26 at 15:41
  • $\begingroup$ Hmmm.... not even an upvote? $\endgroup$ – David G. Stork Mar 26 at 17:31

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