Our graph starts at `t = 0` and has slope `a / b`. It finishes at `t = b`.

So our function will be:

`f(t)=a/b t · {u(t)-u(t-b)}`

The graph of our function:

Graph of `f(t)=a/b t · {u(t)-u(t-b)}`, a sawtooth waveform.