What is cos(0)?

The value of cos(0) is 1.

This is because, in a unit circle, the cosine function represents the x-coordinate of a point on the circle. At the point where the angle is 0 radians (or 0 degrees), the x-coordinate is 1, which means that cos(0) = 1.

Additionally, the cosine function is periodic with a period of 2π, which means that cos(0) = cos(2π) = cos(4π) = ... and so on.