[tex]\it [AB]\equiv [AC] \Longrightarrow \Delta ABC -isoscel \Longrightarrow \widehat{ABC} \equiv \widehat{ACB}\ \ \ \ (1)
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[tex]\it [AB]\equiv [AC] \Longrightarrow AB=AC \Longrightarrow \dfrac{AB}{2} =\dfrac{AC}{2} \Longrightarrow EB = DC \Longrightarrow
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\Longrightarrow [EB] \equiv [DC] \ \ \ \ (2)[/tex]
[tex]Vom \ compara\ \Delta BCE\ cu\ \Delta CBD:
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[tex]\it [BC] \equiv [CB] \ (latura\ comun\breve{a})\ \ \ (*)
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(1) \Rightarrow \widehat{EBC} \equiv \widehat{DCB}\ \ \ \ (**)
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[tex]\it [EB] \equiv [DC] \ \ \ \ \ (***)
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Din\ (*),\ (**),\ (***) \stackrel{LUL}{\Longrightarrow} \Delta BCE \equiv \Delta CBD \Longrightarrow [CE]\equiv [BD] \Longrightarrow
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\Longrightarrow [BD]\equiv [CE] \ \ \ \ \ \ \ [q.\ e.\ d.][/tex]