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May 13, 2025, 05:15:45 pm

Author Topic: Composite functions.  (Read 643 times)  Share 

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bevanweerasinghe

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Composite functions.
« on: March 21, 2013, 05:55:07 pm »
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How do we graph f(g(x)) if f(x)= x(x-a) and g(x)= -|x|
do we split the g(x) into a hybrid function and find f(g(x)) ?

thanks in advance.
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b^3

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Re: Composite functions.
« Reply #1 on: March 21, 2013, 06:18:49 pm »
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Now to work out how to graph our result. Normally if we have , then we'd plot the curve of and then flip everything that is below the axis in the axis. We can do something similar with , except that all the inputs for negative will now have the same output for the corresponding positive value of . That is you would draw the original curve, then take the curve that is on the right side of the axis, copy it and flip it in the axis.

So back to our problem, we can recognise that if we were dealing with say then, . So firstly we should sketch
https://www.desmos.com/calculator/gq69kjxgex
Now we take everything that is on the right hand side of of the axis, https://www.desmos.com/calculator/5bamx2wuau
And copy it, flipping it in the axis.
https://www.desmos.com/calculator/teo9gw6ryq
Which we can see is the same as what we were looking for originally.
https://www.desmos.com/calculator/ebcda7ctrh

Hope that makes sense and hope that helps! :)

Edit: You could probably split it up into a hybrid function, but it'd be a bit more tedious. For me I find that applying the transformations to the curve when working with modulus functions works best, but thats just me. It may or may not be the best method for you.
« Last Edit: March 21, 2013, 06:21:22 pm by b^3 »
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bevanweerasinghe

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Re: Composite functions.
« Reply #2 on: March 21, 2013, 07:12:38 pm »
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Oh that makes so much sense. So basically if we take f(|x|) instead of |f(x)| we reflect everything in the y axis instead of the x axis correct?

Thank you !
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b^3

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Re: Composite functions.
« Reply #3 on: March 21, 2013, 07:25:00 pm »
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Oh that makes so much sense. So basically if we take f(|x|) instead of |f(x)| we reflect everything in the y axis instead of the x axis correct?

Thank you !
For , you take everything for and copy/reflect that across the axis, where as for you take everything that is and flip that in the axis, so theres a slight difference. For the first you keep what you have and copy it, reflecting it over, while for the second, you don't keep what you have below the axis, and flip it up across the axis.
2012-2016: Aerospace Engineering/Science (Double Major in Applied Mathematics - Monash Uni)
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