5.3.2.20 Various Problems in the Space

Condition: in the correct pyramid \ (s a b c d \) the lateral rib forms with the plane of the base the angle equal \ (45^{\ circ} \). At the height \ (s o \) the pyramid is taken point \ (k \) - the middle \ (s o \). Find the angle that forms a straight \ (d k \) with a plane \ (s a d \).