5di was kind of annoying...
Basically, BCP and BAP are similar coz they have equal sides/angles whatever.
And for a 4 sided polygon each interior angle is (n-2)180/5 degrees = 3pi/5
Therefore Angle BAP = 3pi/5 but bap and ead are pi/5 therefore angle cad = pi/5.
Also, Side AC = AP+PC
And...