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The displacement of a damped harmonic oscillator is given by x(t) = e –0.1t cos (10 π t + ϕ ). Here t is in seconds. The time taken for its amplitude of vibration to drop to half of its initial value is close to :

1. 4 s
2. 13 s
3. 7 s
4. 27 s

Correct answer: 7 s

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