numerele a,b,c,d formeaza o proportie daca
[tex] \frac{a}{b} = \frac{c}{d} =K[/tex]
in acest caz
[tex] \frac{9}{18} = \frac{25}{50} = \frac{1}{2} [/tex] deci da se poate forma o proportie
[tex] \frac{a-b}{a+b} = \frac{1}{7} [/tex]
7a-7b=a+b
6a-8b=0
3a-4b=0
3a=4b⇒[tex] \frac{a}{b} = \frac{4}{3} [/tex]