Найдите знаменатель геометрической прогрессии если b1= 81 b7= 1/9
Формула n-го члена геометрической прогрессии:
bₙ = b₁ * qⁿ⁻¹
В данном случае q - знаменатель прогрессии
Подставляем
![\displaystyle\frac{1}{9}=81*q^{7-1}\\\\\\\frac{1}{9}=81q^{6}\\\\\\q^{6}=\frac{1}{9}:81=\frac{1}{9}*\frac{1}{81}=\frac{1}{729}\\\\q=\sqrt[6]{\frac{1}{729} } =\frac{1}{3}](https://tex.z-dn.net/?f=%5Cdisplaystyle%5Cfrac%7B1%7D%7B9%7D%3D81%2Aq%5E%7B7-1%7D%5C%5C%5C%5C%5C%5C%5Cfrac%7B1%7D%7B9%7D%3D81q%5E%7B6%7D%5C%5C%5C%5C%5C%5Cq%5E%7B6%7D%3D%5Cfrac%7B1%7D%7B9%7D%3A81%3D%5Cfrac%7B1%7D%7B9%7D%2A%5Cfrac%7B1%7D%7B81%7D%3D%5Cfrac%7B1%7D%7B729%7D%5C%5C%5C%5Cq%3D%5Csqrt%5B6%5D%7B%5Cfrac%7B1%7D%7B729%7D%20%7D%20%3D%5Cfrac%7B1%7D%7B3%7D "\displaystyle\frac{1}{9}=81*q^{7-1}\\\\\\\frac{1}{9}=81q^{6}\\\\\\q^{6}=\frac{1}{9}:81=\frac{1}{9}*\frac{1}{81}=\frac{1}{729}\\\\q=\sqrt[6]{\frac{1}{729} } =\frac{1}{3}")