Explanation
The Maclaurin series expansion of cos(x) is derived from its Taylor series expansion around x = 0:
cos(x) = 1 - x²/2! + x⁴/4! - x⁶/6! + ...
This series alternates signs and involves even powers of x, with factorials in the denominators.
The answer is cosx = 1 - x²/2! + x⁴/4! - x⁶/6! + ...