Объяснение:
[tex]-27,\ -9,\ -3,\ ...\ \ \ \ \ S_n=?\\q=\frac{-9}{-27}=\frac{1}{3} .\ \ \ \ \Rightarrow\\S_n=a_1*\frac{1-q^n}{1-q}=-27*\frac{1-(\frac{1}{3} )^n}{1-\frac{1}{3} } =-27*\frac{1-(\frac{1}{3})^n }{\frac{2}{3} }=-\frac{81}{2}*(1-(\frac{1}{3} )^n).\\ S_n=-\frac{81}{2}*(1-(\frac{1}{3})^n).[/tex]
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Объяснение:
[tex]-27,\ -9,\ -3,\ ...\ \ \ \ \ S_n=?\\q=\frac{-9}{-27}=\frac{1}{3} .\ \ \ \ \Rightarrow\\S_n=a_1*\frac{1-q^n}{1-q}=-27*\frac{1-(\frac{1}{3} )^n}{1-\frac{1}{3} } =-27*\frac{1-(\frac{1}{3})^n }{\frac{2}{3} }=-\frac{81}{2}*(1-(\frac{1}{3} )^n).\\ S_n=-\frac{81}{2}*(1-(\frac{1}{3})^n).[/tex]