[tex]\displaystyle\bf\\b_{4} =216\\\\q=-3\\\\\\b_{4} =b_{1}\cdot q^{3} \\\\b_{1} =b_{4} :q^{3} =216:(-3)^{3}=216:(-27)=- 8\\\\\\S_{6} =\frac{b_{1}\cdot(1-q^{6} ) }{1-q} =\frac{-8\cdot\Big[1-(-3)^{6} \Big]}{1-(-3)}=\frac{-8\cdot(1-729)}{1+3}=\\\\\\=\frac{-8\cdot(-728)}{4}=-2\cdot(-728)= 1456\\\\\\Otvet \ : \ S_{6} =1456[/tex]
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[tex]\displaystyle\bf\\b_{4} =216\\\\q=-3\\\\\\b_{4} =b_{1}\cdot q^{3} \\\\b_{1} =b_{4} :q^{3} =216:(-3)^{3}=216:(-27)=- 8\\\\\\S_{6} =\frac{b_{1}\cdot(1-q^{6} ) }{1-q} =\frac{-8\cdot\Big[1-(-3)^{6} \Big]}{1-(-3)}=\frac{-8\cdot(1-729)}{1+3}=\\\\\\=\frac{-8\cdot(-728)}{4}=-2\cdot(-728)= 1456\\\\\\Otvet \ : \ S_{6} =1456[/tex]