427. Can the sides of a right triangle form an arithmetic progression? a geometric progression?
427. 
$$
\begin{aligned}
& a) Only } 3,4,5 ; \text { b) progression with common ratio } \\
& \sqrt{\frac{1+\sqrt{5}}{2}}, \text { specifically: } 1, \sqrt{\frac{1+\sqrt{5}}{2}}, \frac{1+\sqrt{5}}{2}
\end{aligned}
$$