Notam ABCD paralelogramul
ducem inaltimile h=CE= DF perpendiculare pe AB
BE=AF=x
FB=42-x
h²=80²-(42+x)²
h²=52²-(42-x)²
80²-(42+x)²=52²-(42-x)²
6400-1764-84x-x²=2704-1764+84x-x²
4636-84x=940+84x
168x=3696
x=22
h=√[52²-(42-22)²]=√(2704-400)=√2304=48 cm
AD=CB=√(48²+22²)=√(2304+484)=√2788=2√697 cm
P=42x2+2√697x2=84+4√697
A=42x48=2016 cm²