Răspuns :

Răspuns:

[tex]\frac{a}{n} =\frac{b}{n+1}=\frac{c}{n+2}[/tex]

[tex]a=\frac{nb}{n+1}[/tex]

[tex]c=\frac{nb+2b}{n+1}[/tex]

[tex]a+c=\frac{nb}{n+1}+\frac{nb+2b}{n+1}  =\frac{2b(n+1)}{n+1} =2b[/tex]

[tex]\frac{a+c}{2}=b[/tex]

Explicație pas cu pas:

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