pole ΔAPD −−− S1
pole ΔCPD −−− S2
pole Δ ABP −−− S3
PΔABD = S1 +S3 = 12a*h
S3 = 12*IPEI
S2= 12a*IPFI IPEI +IPFI= h
to
S3 + S2= 12*a( IPEI+IPFI)= 12a*h
to:
S1+S3 = S3 +S2 => S1 = S3 −S3 +S2
to S1= S2 więc PΔ APD= PΔCPD
c. b.d.o
S3= 12*a*IPEI