Arccos(x), cos-1(x), inverse cosine function.
The arccosine of x is defined as the inverse cosine function of x when -1≤x≤1.
When the cosine of y is equal to x:
cos y = x
Then the arccosine of x is equal to the inverse cosine function of x, which is equal to y:
arccos x = cos-1 x = y
Here cos-1 x means the inverse cosine and does not mean cosine to the power of -1.
arccos 1 = cos-1 1 = 0 rad = 0°
Graph of arccos