`f(0) = 4` means we start at value `4`.

If the whole wave has period `2`, and it is a square wave, then it means for half of the time, the value is (positive) `4` and the other half it is `-4`.

So for the first second, it has value `4`, for the second second, the function value is `-4`.

We write this, using the "rectangular pulse" formula from before:

`f(t) = 4·{u(t) − u(t − 1)}` `-4·{u(t-1) − u(t − 2)}`

`=4·u(t)-8·u(t-1)+4·u(t-2)`

The graph of this first cycle is:

0.511.522.5-0.5-11234-1-2-3-4tf(t)Open image in a new page

Graph of `f(t)=4·u(t)-8·u(t-1)+4·u(t-2)`, a square wave.

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