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A particle undergoing simple harmonic oscillation moves according to the equation:

$$ x(t) = A \cos (3t) $$

What is the acceleration of the particle as a function of time?

$ 9A \cos (3t) $

$ -9A \cos (3t) $

$ 9A \sin 3t $

$ -9A \sin (3t) $

$ -9A^2 \sin(3t) $