trying to define a periodic function with the (if then) command

Hi, I'm doing a work for school and I'm failing to represent the function
properly.

Here's the problem:
I want to determine the Fourier series of a signal vi(t) = va(t) + vb(t)

vb(t) is given, but va(t) is only given half of the period and it's said
that va(t) is a pair function(symmetry towards the y axis).

va(t) is represented:
3*sin(%pi/2*t)         for     0<t<1
3-3*sin(%pi/4(t-1))   for    1<t<3/2

What i think i need, is to represent va(t) as a periodic function. In the
file I attached va(t) isn't working at the part:
"if t>-3/2 and t<-1 then -va2(t)"  the graph of the function doesn't
represent that part.

Then it's the problem of making that function a periodic one.

thanks
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