Răspuns:
13
Explicație pas cu pas:
[tex]10^{2n+1}:5^{2n+1}=8^{9}\\(10:5)^{2n+1}=8^{9}\\2^{2n+1}=(2^{3})^{9}\\2^{2n+1}=2^{27}\\2n+1=27, 2n=27-1, 2n=26, n=26:2, n=13[/tex]
