Answer
$\displaystyle \frac{x-7}{x+7}$
Work Step by Step
Simplifying Rational Expressions
1. Factor the numerator and the denominator completely.
2. Divide both the numerator and the denominator by any common factors.
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Numerator: recognize a square of a binomial
$(x-7)^{2}$
Denominator: recognize a difference of squares
$(x+7)(x-7)$
Expression = $\displaystyle \frac{(x-7)^{2}}{(x+7)(x-7)}$
... divide both with the common factor: $(x-7)$
Expression = $\displaystyle \frac{x-7}{x+7}$