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Review: Substitution Into an Expression
Explanation
This question could be solved the old-fashioned way by
plugging in 
for x
in the original expression and simplify it, primarily by multiplying it by
versions of 1. That will be fairly work-intensive, however. We can try picking
a specific case and seeing which answer choices match it.
Say 
.
In that case,
and 
.
We can therefore plug 
in for y
in the answer choices and see which of them generate 9. Any that do not can't
be the correct answer. (A) yields 
So it could be correct. (B) is the inverse, so it will
give 
and it's out. (C) gives 
over 
,
which is not 9. (D) and (E) are both negative, so they are not 9.
The correct answer is (A).
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