Sa se calculeze suma 1+1/3+1/3^2+1/3^3+1/3^4

Răspuns :

[tex] 1+\frac{1}{3}+\frac{1}{3^{2}}+\frac{1}{3^{3}}+\frac{1}{3^{4}}= [/tex]
[tex] =\frac{3^{4}}{3^{4}}+\frac{3^{3}}{3^{4}}+\frac{3^{2}}{3^{4}}+\frac{3}{3^{4}}+\frac{1}{3^{4}}= [/tex]
[tex] =\frac{1+3+3^{2}+3^{3}+3^{4}}{3^{4}}= [/tex]
[tex] =\frac{\frac{3^{5}-1}{2}}{3^{4}}= [/tex]
[tex] =\frac{3^{5}-1}{2*3^{4}}= [/tex]
[tex] =\frac{243-1}{2*81}= [/tex]
[tex] =\frac{242}{162}=\frac{121}{81} [/tex]