AB = BC=CD=AD = 5cm
Notam cu O intersectia diagonalelor AC si BD.
In Δ AOB, dr. in O :
m(A) = 60 grade
m(B) = 30 grade
AO = AB/2 =5/2
⇒AC = 2AO =5 cm (diagonala mica)
BO² = AB²-AO²
BO² = 25 - 25/4
BO² = 75/4
BO = 5√3/2 cm
BD = 2BO = 5√3 cm (diagonala mare)
A = d1 × d2 /2 = 5× 5√3 / 2 =25√3/2 cm²