5. Given a fixed point $A(3,0), B(0,4), P$ is a moving point on the incircle of $\triangle A O B$ ( $O$ is the origin), then the maximum value of $|P A|^{2}+$ $|P B|^{2}+|P O|^{2}$ is $\qquad$ .
5. 22 It is easy to see that the equation of the inscribed circle is $(x-1)^{2}+(y-1)^{2}=1, P(1+\cos \theta, 1+\sin \theta)$, then $|P A|^{2}+|P B|^{2}+$ $|P O|^{2}=(\cos \theta-2)^{2}+(1+\sin \theta)^{2}+(1+\cos \theta)^{2}+(3-\sin \theta)^{2}+(1+\cos \theta)^{2}+(1+\sin \theta)^{2}=20-2 \sin \theta$ $\leqslant 22$ (when $\sin \theta=-1$ the equality holds)