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2014-02-13T21:49:06+02:00
AC=BD sunt diagonale de trapez
BD=20
BD=DO+OB
DO/OB=3/7
DO/BD-DO=3/7
DO/20-DO=3/7
3(20-DO)=7DO
60-3DO=7DO
-3DO-7DO=-60
-10DO=-60
10DO=60
DO=6  OB=14
2 3 2