Sum[(-1)^k * (2^n)^(2 * k) * ArcCos[x]^(2 * k) / Factorial[2 * k], {k, 0, Infinity}]Sum[(-1)^k * (2^n)^(2 * k) * ArcCos[x]^(2 * k) / Factorial[2 * k], {k, 0, Infinity}]

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