Suppose, α is the angle between hypotenuse and its adjacent side. Then, the measure of angle α is given by;
α = cos-1 (adjacent side of α/hypotenuse)
Where cos-1 represents the cos inverse function.
Let α is an angle equal to cos-1 (0)
α = cos-1(0)
We know that, cos 90 degrees = 0
Therefore, α = cos-1 (cos 90) = 0 degrees= ∏/2
cos-1 (0)= ∏/2