= Solution
In the right-hand <classically allowed region>, put $p(x)=\sqrt{2m[E-V(x)]}$ and $s(x)=\hbar^{-1}\int_{x_1}^xp(y)\,dy$. A convenient form of the general <WKB approximation> is
$$
\boxed{\psi_{\rm II}(x)\simeq\frac{C\cos(s(x)+\pi/4)+D\sin(s(x)+\pi/4)}{\sqrt{p(x)}},\qquad x_1<x<x_2.}
$$
The phase origin $\pi/4$ is a choice of <basis> for the two oscillatory solutions, anticipating the <Airy turning-point connection formula>. Equivalently, one may use independent $e^{is}$ and $e^{-is}$ branches. The coefficients have not yet been related to those in either forbidden region.
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