Answer
a) $(1+\sqrt2)s$
b) $2s^2 (1+\sqrt2)$
Work Step by Step
a) The length of the diagonal is equal to:
$$ l = \frac{\sqrt{2}}{2}s + \frac{\sqrt{2}}{2} s + s \\ =(1+\sqrt2)s$$
b) The area of a regular octagon is equal to:
$$ A = 2s^2 ((1+\sqrt2)$$
