Ответ: n=3.
Объяснение:
b₁=3 b₂=9 Sₙ=39 n=?
[tex]\displaystyle\\q=\frac{b_2}{b_1} =\frac{9}{3} =3.\\\\S_n=b_1*\frac{q^n-1}{q-1} =3*\frac{3^n-1}{3-1} =\frac{3}{2}*(3^n-1)=39\\\\\frac{3}{2} *(3^n-1)=39\ |*\frac{2}{3} \\\\3^n-1=26\\\\3^n=27\\\\3^n=3^3\ \ \ \ \ \ \Rightarrow\\\\n=3.[/tex]
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Ответ: n=3.
Объяснение:
b₁=3 b₂=9 Sₙ=39 n=?
[tex]\displaystyle\\q=\frac{b_2}{b_1} =\frac{9}{3} =3.\\\\S_n=b_1*\frac{q^n-1}{q-1} =3*\frac{3^n-1}{3-1} =\frac{3}{2}*(3^n-1)=39\\\\\frac{3}{2} *(3^n-1)=39\ |*\frac{2}{3} \\\\3^n-1=26\\\\3^n=27\\\\3^n=3^3\ \ \ \ \ \ \Rightarrow\\\\n=3.[/tex]