Question 971505
see my worksheet below:


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the answer key is correct except there should be a minus sign there as well which i don't see.


121 - x^2 is equal to (11-x) * (11+x)


x^2 - 18x + 77 is equal to (x-11) * (x-7)


(11-x) in the numerator is equivalent to -(x-11) which then cancels out with the (x-11) in the denominator and leaves a -1 because -(x-11) / (x-11) = -1.