Final answer:
Without a complete sequence for x₁[n], the exact output for x₂[-n] + x₁[n] cannot be computed. However, we can explain the operation involved and provide a partial answer.
Step-by-step explanation:
The student's question requires finding the output for x₂[-n] + x₁[n], given the signals x₂[n] = [1, 2, -1, 3] and an incomplete sequence for x₁[n]. Unfortunately, x₁[n] is not fully defined as we only have two elements: [z, -23, ...]. Without the complete sequence for x₁[n], we cannot compute the exact output for the given expression. However, we can demonstrate how the operation would be performed if both sequences were fully known.
To find x₂[-n], you would flip the signal x₂[n] around the origin, which results in reversing the order of elements in the sequence. This would change x₂[n] = [1, 2, -1, 3] to x₂[-n] = [3, -1, 2, 1].
To find the sum x₂[-n] + x₁[n], you would then add the elements of x₂[-n] to the corresponding elements of x₁[n]. Since x₁[n] is incomplete, we can only say that the sum at the first position would be 3 + z, and at the second position, it would be -1 + (-23).