S=sqrt(p(p-a)(p-b)(p-c))
p=P\2
P=13+14+15=42 =>p=21
S=sqrt(21(21-13)(21-14)(21-16))=sqrt(21*8*7*6)=sqrt(7056)=84
S=sqrt(p(p-a)(p-b)(p-c))
p=P\2
P=13+14+15=42 =>p=21
S=sqrt(21(21-13)(21-14)(21-16))=sqrt(21*8*7*6)=sqrt(7056)=84