<h3>
Answer: C) 4</h3>
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Work Shown:
Expand out the left hand side
(x-k)(x-5)
x(x-5)-k(x-5)
x^2-5x-kx+5k
Note that the constant term here is 5k. Yes k seems like a variable, but it's actually a constant. Once we know k, we can replace it to get a fixed number. In this case, k = 4 since 5k = 5*4 = 20 to have it match with the 20 at the end of x^2-9x+20
For the x terms, we have -5x-kx = -5x-4x = -9x which matches with the middle term of x^2-9x+20
Therefore,
(x-k)(x-5) = x^2-9x+20
updates to
(x-4)(x-5) = x^2-9x+20
The -4 and -5 multiply to 20, and they also add to -9. This helps confirm we have the right k value.
