Question

Which one of the following discrete-time systems is time-invariant?

• A. \( y(n) = nx(n) \)
• B. \( y(n) = x(3n) \)
• C. \( y(n) = x(-n)\pi \)
• D. \( y(n) = x(n-3) \)

Hint:

Test time invariance: shift input, check if output shifts identically.

Answer 1

The Correct Option is D

Time invariance means delay in input causes equivalent delay in output. Only option (4) satisfies this: Delay input → output delays accordingly.