daca un patrulater are toate laturile congruente se numeste romb
KB=AB-AK=5, DP=DC-PC=5
AKD tr dreptunghic, cu t lui Pitagora se calculeaza DK=5
BPC tr. dreptunghic, cu t Pitagora se calculeaza BP=5
KB≡DP≡DK≡PB, deci KBPD romb
Aria BCD=BCxCD/2=4x5/2=10
aria BCP=BCxPC/2=4x3/2=6
aria DPB=aria BCD-aria BCP-10-6=4
aria KBPD=2xariaDPB=8