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2014-08-07T18:46:55+03:00
ABCD-romb
AB=BC=CD=AD=6

ΔABC
AB=AC
mas<A=60   ⇒ΔABC-echilateral

A ABCD=2*A ΔABC

A ΔABC=l²√3/4=  6²√3/4= 36√3/4=  9√3

A ABCD=2* 9√3= 18√3