Solution
= Solution
For $x'=\Lambda x$, a <Dirac spinor> transforms as
$$
\psi'(x')=S[\Lambda]\psi(x).
$$
Hence
$$
\partial'_\mu\psi'(x')
=(\Lambda^{-1})^\nu{}_\mu S[\Lambda]\partial_\nu\psi(x).
$$
Using the result of part i, the <Dirac adjoint> transforms as
$$
\boxed{\overline\psi'(x')=\overline\psi(x)S[\Lambda]^{-1}}.
$$