Question

Помогите пожалуйста!!!​

Answer 1

$b_{3} =4\\\\q=\frac{2}{3}\\\\b_{3}=b_{1}*q^{2}\\\\b_{1}=b_{3}:q^{2}=4:(\frac{2}{3})^{2}=4*\frac{9}{4}=9\\\\S=\frac{b_{1} }{1-q}=\frac{9}{1-\frac{2}{3}}=\frac{9}{\frac{1}{3} }=27\\\\\boxed{S=27}$