Linia mijlocie în trapez=(B+b)/2
[tex]a) \frac{8+4}{2} =6[/tex]
[tex]b) \frac{2 \sqrt{7}+6 \sqrt{7} }{2} =4 \sqrt{7} [/tex]
[tex]c)6,(3)=6 \frac{3}{9} = \frac{19}{3} \\ 9,(3)=9 \frac{3}{9} = \frac{28}{3} \\ \frac{19}{3} + \frac{28}{3}= \frac{47}{3} \\ \frac{ \frac{47}{3} }{2} = \frac{94}{3} [/tex]