5. (a) A vector field
F (z) = U(x, y) + iV (I, y)
is said to be irrational if
U, (I, y) = V2 (I, y)
, it is said to be solenoidal if
Ux T, y) = -V, (I, y)
_ If
f (z)
is a holomorphic function, show that
F（2） =f（2）
is both irrutional and solennidal (15 Marks).