#### Answer

one-to-one

#### Work Step by Step

See p.408, Tests to Determine Whether a Function Is One-to-One
1. Show that $f(a)=f(b)$ implies $a=b$.
This means that $f$ is one-to-one.
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$y=f(x)=2x-8$
Assume that $f(a)=f(b)$
$\ \ \Rightarrow \ \ 2a-8=2b-8\qquad /+8$
$\ \ \Rightarrow \ \ 2a=2b\qquad /\div 2$
$\ \ \Rightarrow \ \ a=b$
$f$ is one-to-one