The correct option is A 3
The signal y(n)=x(n)∗h(n)
=∑∞k=−∞x(k).h(n−k)
In this case, this summation reduces to
y(n)=∑8k=0x(k).h(n−k)=∑8k=0h(n−k)
h(n)=0 for,n>N[N+1,samples are there]
x(n)=0 for,n>8[9 samples are there]
y(n)=0 for,n>(9+N−1)[9+N+1−1=9+Nsamplesthere]
y(n)=0 for,n>8+N
Given that,
y(n)=0for,n=12
∴12>8+N
4 > N
∴N<4
From here, we may conclude that N can atmost be 3
Given that, y(4) = 4
y(4)=∑8k=0h(4−k)
4=h(4)+h(3)+h(2)+h(1)+h(0)+h(−1)+h(−2)+h(−3)+h(−4)
4=h(4)+h(3)+h(2)+h(1)+h(0)
and this equation satisfies only when,
h(0)=h(1) = h(2) = h(3) = 1
and h(4) = 0
∴h(n)=1,for 0≤n≤3
∴ N = 3