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Cel mai inteligent răspuns!
2014-08-01T13:16:26+03:00
7.
Daca  AC||DE, si E∈AB, DC|| AB=> DC||EA=>
EDCA =paralelogram
Daca DB_|_AC, ⇒ DB_|_ ED;

Daca EDCA =paralelogram=> EA=DC=4
In ΔDEB, DA_|_ EB, si <EDC=90
=> DA= inaltime⇒
DA²=EA*AB=4*9=36
DA=6

Aria trapezABCD=(AB+DC)*AD/2=(9+4)*6/2=39
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6.
Aria romb=d1*d2/2=24
=> d1*d2=48
n*3*n*4=48
n²=48/12=4
n=2
d1=2*3=6
d2=2*4=8