[tex] \it m(\hat{C}) = 60^o\ (complementul\ lui\ 30^o) \ \ \ \ \ \ (1)
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D\ este\ simetricul\ lui \ C\ fa\c{\it t}\breve{a} \ de\ A \Rightarrow AD = AC\ \ \ \ \ (2)
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BA\perp CD \ \ \ \ \ \ (3)
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(2), (3) \Rightarrow BA - median\breve{a}\ \c{s}i\ \^{i}n\breve{a}l\c{\it t}ime\ pentru\ triunghiul\ BCD \Rightarrow [/tex]
[tex] \it \Rightarrow Triunghiul\ BCD- isoscel\ \ \ \ \ (4)
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(1), (4) \Rightarrow Triunghiul\ BCD- echilateral [/tex]
