a)
[tex]
\it EF || BC \Rightarrow \widehat{EBC} \equiv \widehat{FEB} \ (alterne\ \ interne) \ \ \ \ (1)
\\ \\
BE -bisectoare \ \Rightarrow \widehat{EBC} \equiv \widehat{EBF} \ \ \ \ \ (2)
\\ \\
(1),\ (2) \Rightarrow \widehat{FEB} \equiv \widehat{EBF} \Rightarrow \Delta FBE - isoscel \Rightarrow BF = EF = 18\ cm [/tex]
b)
[tex] \it EF || BC \Rightarrow \widehat{ACB} \equiv \widehat{AEF} \ (corespondente) \Rightarrow m(\widehat{ACB}) = m(\widehat{AEF}) =47^o
\\ \\ \\
m(\hat A) = 180^o- m(\hat B) -m(\hat C) =180^o -86^o-47^o = 47^o [/tex]
