SOLUTION: State the vertical, horizontal asymptotes and zeros of the rational function, f(x) = (x^2 + 3x + 2)/(x^2 + 5x + 4) Why is there no zero at x = –1?

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Question 987330: State the vertical, horizontal asymptotes and zeros of the rational function, f(x) = (x^2 + 3x + 2)/(x^2 + 5x + 4)
Why is there no zero at x = –1?

Answer by Edwin McCravy(20055)   (Show Source): You can put this solution on YOUR website!
Instead of doing your problem for you, I'll do one exactly in every detail
like yours so that you can do yours yourself using this as a model.  You
won't learn it as well if I do it for you. I'll do this one instead:

State the vertical, horizontal asymptotes and zeros of the rational function,

Why is there no zero at x = –3?
First we'll get the horizontal asymptote's equation:

Since the numerator and denominator have the same degree, the horizontal
asymptote's equation is 
   
That's



Now let's answer the question "Why is there no zero at x = –3?"
Let's substitute -2 for x and see:






One of the impossible things in mathematics is division
by zero.  So that's why I crossed this out, and it's why f(-3)
is not a zero.

Now we'll go back and find the vertical asymptotes



We factor numerator and denominator:



Now since the (x+3)'s will cancel, that will give us another function g(x)
which is exactly like f(x) except it WILL have a zero at x=-3 whereas f(x)
does not have a zero there:

So we get



And we find the vertical asymptote's equation by setting the denominator = 0:

x+4 = 0

So the vertical asymptote's equation is x = -4

Now we graph g(x) by graphing the horizontal and vertical asymptotes (in green)
and making a table of values:

 x   y
-14  2.5
-9   3
-5   7
-3  -3
 0   1
 6  1.5    
  


That's the graph of g(x) but the graph of f(x) must
have a hole at (-3,-3) because that's not part of the
graph:



Edwin


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