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Can the polynomial in the numerator of the expression x^2-5x+7/x-9 be factored to derive (x-9) as a factor?

User Junep
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1 Answer

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The answer is no.

Explanation #1
Define the numerator as
f(x) = x^2 - 5x + 7.

If (x-9) is a factor, then x=9 will be a zero of f(x), so that f(9)=0.
f(9) = 9^2 - 5*9 + 7 = 43
Because f(9)≠0, (x-9) is not a factor of f(x).

Explanation #2
Perform long division.

x + 4
-------------------------
x-9 | x^2 - 5x + 7
x^2 - 9x
----------------------
4x + 7
4x - 36
-----------
43

Because there is a remainder of 43, the numerator cannot be factored with (x-9) as a factor.
User Luqi
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