The given parabolas are symmetric about the line y=x

Tangents at A& B must be parallel to y=x line, so slope of the tangents =1
(dxdy)minA=1=(dxdy)minB
For point B,y=x2+2
$\begin{gathered}
\frac{d y}{d x}=2 x=1 \
x=\frac{1}{2} \Rightarrow y=\frac{9}{4} \
\therefore \text { Point } B=\left(\frac{1}{2}, \frac{9}{4}\right) \Rightarrow \text { Point } \mathrm{A}=\left(\frac{9}{4}, \frac{1}{2}\right) \
\mathrm{AB}=\sqrt{\left(\frac{1}{2}-\frac{9}{4}\right)^2+\left(\frac{9}{4}-\frac{1}{2}\right)^2} \
=\sqrt{\frac{98}{16}}=\frac{7 \sqrt{2}}{4}
\end{gathered}$
Radius ==872