ISRO EC 2025 Q.4: official answer

ISRO 2025 · ECQ.4 · 1 mark · MCQ

Which of the three signals given below is periodic?
$x_{1} (t) = 2 e^{j (t + \frac{π}{4})} u (t)$
$x_{2} (n) = u [n] + u [- n]$
$x_{3} (t) = \sum_{k = - \infty}^{\infty} {δ [n - 4 k] - δ [n - 1 - 4 k]}$

(A)
$x_{1} (t)$
(B)
$x_{2} (n)$
(C)
$x_{3} (t)$
(D)
None of the above

See the question in the paper

ISRO EC 2025 question 4

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Official answer

Official answer: DSource: ISRO's final answer key of 15 May 2026

From the ISRO EC 2025 paper. Every question of this paper · The full paper (PDF, ISRO) · All 2 ISRO Signals basics questions, with notes