Rational function transformation

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Discussion Overview

The discussion revolves around the transformation of the rational function \( y = -\frac{5x + 18}{x + 4} \) into a form that highlights its relationship to the basic function \( y = \frac{1}{x} \). Participants explore how to express this function in terms of vertical and horizontal shifts, as well as vertical stretching.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant suggests that the function is shifted 4 units to the left and stretched by a factor related to the numerator, but seeks further elaboration.
  • Another participant proposes rewriting the function in the form \( y(x) = a\frac{1}{x-b} + c \) to identify the transformations, noting the need to manipulate the numerator.
  • A participant questions the relevance of factoring the numerator in achieving the desired form, expressing confusion about how it relates to the vertical shift.
  • One participant provides a division approach to rewrite the function, suggesting it can be expressed as \( -\left(5 + \frac{-2}{x + 4}\right) \) and asks how this compares to the transformation form.
  • Another participant expresses confusion about the equality of two expressions and the treatment of the constant term 18 during the transformation process.
  • A later reply attempts to clarify the transformation by showing the function can be rewritten as \( \frac{2}{x+4} - 5 \), identifying the vertical stretch, horizontal shift, and vertical shift.
  • Another participant emphasizes the need for long division to arrive at a suitable equation for further analysis.

Areas of Agreement / Disagreement

Participants exhibit varying levels of understanding and approaches to the problem, with no consensus reached on the best method to express the transformations or the implications of the numerator's manipulation.

Contextual Notes

Some participants express uncertainty about the steps taken to rewrite the function, particularly regarding the treatment of constants and the division process. There are unresolved questions about how to accurately represent the transformations in relation to the basic function.

woof123
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the question is: Rewrite the rational equation y=(-5x-18)/(x+4) to show how it is a transformation of y=1/x. describe transformations

looks like it is shifted 4 to left, then stretched by factor of -5x-18. Is that accurate? would you elaborate beyond that?
 
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We are given:

$$y=-\frac{5x+18}{x+4}$$

And to show this is a transformation of:

$$f(x)=\frac{1}{x}$$

We need to write $y$ in the form:

$$y(x)=a\frac{1}{x-b}+c$$

where $a$ is the vertical stretching factor, $b$ is the horizontal shift, and $c$ is the vertical shift.

So, I would observe that:

$$5x+18=5(x+4)-2$$

Can you continue?
 
sorry but I don't see how factoring the numberator helps get it into the form you described.[desmos="-10,10,-10,10"]y=-(5x+18)/(x+4)[/desmos] I see the function is shifted left 4 (as accomplished by the denominator but I'm not understanding how the numerator gets it shifted down 4 (approx). Is the numberator you have now factored considered "c"?
 
What MarkFL is saying is that you need to change the form of your function. So do some division:
[math]y = - \frac{5x + 18}{x + 4} = - \left ( 5 + \frac{-2}{x + 4} \right )[/math]

How do you compare this with [math]a \frac{1}{x - b} + c[/math]?

-Dan
 
sorry but i don't understand how those two expressions are equal. what happened to the 18
 
woof123 said:
sorry but i don't understand how those two expressions are equal. what happened to the 18
I'm not quite good enough with tables to show you the division, so I'll prove it backward:
[math]5 + \frac{-2}{x + 4} = \frac{5(x + 4)}{x + 4} + \frac{-2}{x + 4}[/math]

[math] = \frac{5(x + 4) - 2}{x + 4} = \frac{5x + 20 - 2}{x + 4} = \frac{5x + 18}{x + 4}[/math]

This site has a worked example. You should have done this in either the class you are taking now or previously.

-Dan
 
This is what I intended for you to do:

$$y=-\frac{5x+18}{x+4}=-\frac{5(x+4)-2}{x+4}=\frac{2}{x+4}-5$$

And so we see that the vertical stretch is 2, the horizontal shift is 4 units to the left, and the vertical shift is 5 units down.
 
Just do the long division. After that, you should arrive with an equation that allows division by x + 4.
Such equation should be something like -(5x + 18) = . . ..
 

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