Is it true that for any real valued function $f(t)$ on $\mathbb{R},$ $f(t)a + (1-f(t))b$ is also a line contained in $L$? [closed]

I have the following doubt.

We know that for any two points $a$ and $b,$$L=ta+(1-t)b$ represents a line joining $a$ and $b.$ Is it true that for any real valued function $f(t)$ on $\mathbb{R},$$f(t)a + (1-f(t))b$ is also a line contained in $L$? I think the answer is yes.