9.ΔDAB:AD=AB
ΔABC:AB=BC
m(∡BDA)=m(∡BAC)
Rezulta prin LUL ca ΔDAB≡ΔABC⇒AC=BD⇒ABCD=patrat
10a)Analog se arata ca m(∡CEF)=m(∡CDB)=45°⇒EF//BD (corespondente)
b)Avem ca m(∡CPF)=m(∡CAB)=45°
m(∡APF)=360-m(<PAB)-m(<ABF)-m(<BFP)
m(∡APF)=360-45-90-90
m(<APF)=135°
m(<APC)=m(<APF)+m(<CPF)
m(<APC)=135+45
m(<APC)=180°⇒A,P,C coliniare
