Find the circulation and flux of the field F = xi +yj around and across the closed semicircular path that consists of the semicircular arch r₁(t)=(a cos t)i+(a sin t)j,O ≤ t ≤ π, followed by the line segment r₂(t)= ti, -a ≤ t ≤ a. The circulation is. (Type an exact answer, using t as needed.)