Correct Answer - Option 4 : -1 < a < 0
Real exponentials: real exponential contains no imaginary numbers and are expressed simply as
\(f\left( n \right) = B{e^{\alpha n}}\)
Where both B and α are real parameters. Unlike complex exponential that oscillates, the real exponential either decays or grows depending on the value of α.
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Decaying exponential, when α < 0
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Growing exponential, when α > 0
Hence, from the given options, -1 < a < 0 represents the double-sided decaying exponential signal.
