3) [tex] \frac{a+3b}{2a+5b} = \frac{5}{9}[/tex]⇒9a+27b=10a+25b |-25b-9a ⇒ 2b=a (1)
[tex] \frac{3b+c}{b+4c} = \frac{10}{7} [/tex]⇒ 21b+7c=10b+40c |-7c-10b⇒ 11b=33c |÷11 ⇒ b=3c (2)
Din (1) si (2)⇒ a=6c
[tex] \frac{a+b-c}{3a-b+c} = \frac{c(6+3-1)}{c(18-3+1)} = \frac{8}{16} = \frac{1}{2} [/tex]
Pe 5 nu il pot face, scuze
