In other words, if $f(x_1) = f(x_2)$, then $x_1$ must equal $x_2$. Let's check this for the given function:
$f(x_1) = x_1 + 5$
$f(x_2) = x_2 + 5$
If $f(x_1) = f(x_2)$, then:
$x_1 + 5 = x_2 + 5$
Subtracting 5 from both sides, we get:
$x_1 = x_2$
Since $x_1$
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