Challenge for the Weak 2 - P3

Contributed by: cauchy

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Difficulty: 9

This problem is tagged with cw, cw2.

Consider the following product: $$ p_n = \prod_{k=1}^{n} \cos(2^{k-1}x), \quad x \neq k\pi. $$ Find the limit: $$ \lim_{n \to \infty} p_n $$ A. $1$
B. $\frac{\cos{x}}{x}$
C. $0$
D. $\frac{\sin{x}}{x}$
E. does not exist
Your answer should be a single capitalized letter, e.g., 'A'.

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