Mark M. answered 11/16/18
Retired math prof. Calc 1, 2 and AP Calculus tutoring experience.
dy/dx = 1 / √(4 - x2)
Separate variables: dy = 1 / √(4 - x2) dx
Integrate: ∫dy = ∫ [1 / √(4 - x2)]dx
So, y = Sin-1(x/2) + C
Since y = π when x = 0, π = Sin-1(0) + C
C = π
y = Sin-1x + π