The function cos(x) is an even function. This means that it satisfies the condition:
f(-x) = f(x)
For cosine, if we take the cosine of the negative angle, we find:
cos(-x) = cos(x)
This equality shows that for every angle x, the cosine value remains the same whether the angle is negative or positive. Therefore, since cos(x) meets the criteria for being an even function, we conclude that it is indeed even.