Answer
Yes, f(x) is one-to-one.
Work Step by Step
The function $f(x)=-2x+4$ is one-to-one because it is a diagonal line and passes the horizontal line test. We can show this algebraically:
We start with the assumption that:
$x_1\ne x_2$
Then:
$-2*x_1\ne -2*x_2$
And:
$-2*x_1+4\ne -2*x_2+4$
So the function would not have the same $y$ value for two different $x$ values (one-to-one).
