SOLUTION: Explain why -5, 9, and -4 are not allowable replacements for the variable x in the following problem: x-8/x+5 divide by x-9/x+4 Help!! I don't know what to do with this one.

Question 102142: Explain why -5, 9, and -4 are not allowable replacements for the variable x in the following problem:
x-8/x+5 divide by x-9/x+4
Help!! I don't know what to do with this one. Thank you very much.
Answer by jim_thompson5910(35256) (Show Source): You can put this solution on YOUR website!
Start with the given expression

Multiply the first fraction by the reciprocal of the second fraction

Plug in x=9 (this is one of the given values)

Combine like terms. Since you cannot divide by zero, x=9 is not valid for this expression

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Now let's look at the first fraction

Plug in x=-5 (this is one of the given values)

Combine like terms. Since you cannot divide by zero, x=-5 is not valid for this expression

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Now let's look at the second fraction

Plug in x=-4 (this is one of the given values)

Combine like terms. Since you cannot divide by zero, x=-4 is not valid for this expression

So essentially, all 3 of these x values produce denominators of zero. This means they produce undefined results
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