[tex]\it \dfrac{a}{b} = 0,(2) \Rightarrow \dfrac{a}{b} = \dfrac{2}{9} \Rightarrow \dfrac{b}{a} = \dfrac{9}{2} \Rightarrow \dfrac{b}{a} = 4,5 \Rightarrow b = 4,5a \ \ \ \ (*)
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\dfrac{2a}{b-2a} = \dfrac{2a}{4,5a-2a} = \dfrac{2a}{2,5a} = \dfrac{^{4)}2}{\ 2,5}= \dfrac{8}{10} = 0,8[/tex]
