Find the circulation and flux of the field Bold Upper F equals negative 3 x squared Bold i minus 3 y squared Bold j around and across the closed semicircular path that consists of the semicircular arch Bold Bold r 1 (t )equals (a cosine t )iplus (a sine t )j, 0 less than or equals t less than or equals pi, followed by the line segment Bold r 2 (t )equals t Bold i, negative a less than or equals t less than or equals a.