I assume your question amounts to finding the period of f(t)=8sin(4 pi t). A period L is a positive number such that f(t+L)=f(t) for all t. Since sin(x) is 2 pi perodic we can find the least number L such that 4pi(t+L)=4*pi*t+2*pi. Multiplying out we get
4pi(t+L)=4*pi*t+4*pi*L and we want to find L such that we get 4*pi*t+2*pi, notice if we take L=1/2 we get the desiered result 4*pi*t+4*pi*1/2=4*pi*t+2*pi. This proves that L=1/2 and your function has a period of 1/2.
