The function \cos(x) is a fundamental trigonometric function that represents the cosine of an angle x. It is defined for all real numbers and is commonly used in mathematics, physics, and engineering. The output of \cos(x) ranges from -1 to 1, and it is periodic with a period of 2\pi, meaning it repeats its values every 2\pi radians. In a right triangle, \cos(x) is the ratio of the length of the adjacent side to the hypotenuse. This relationship is crucial in various applications, including geometry, wave motion, and signal processing. The graph of \cos(x) is a wave-like curve that oscillates between -1 and 1, illustrating its periodic nature.