The function "cos(x)" represents the cosine of an angle "x" measured in radians. It is a fundamental concept in trigonometry, which studies the relationships between the angles and sides of triangles. The cosine function outputs values between -1 and 1, indicating the horizontal coordinate of a point on the unit circle corresponding to the angle "x". In practical applications, "cos(x)" is used in various fields such as physics, engineering, and computer graphics. It helps model periodic phenomena, like sound waves and light waves, and is essential for analyzing oscillations and rotations. Understanding "cos(x)" is crucial for solving problems involving angles and distances.