acos(sqrt(2)/2)
Let's calculate: acos(22)
ⓘ acos, asin and atan give the principal angle whose cosine, sine or tangent respectively equals the number, here a remarkable value: acos(22) = π4
▶Result:   π4
The numeric value of: π4 is:
≈ 3.14164
▷ ≈ 0.7854