Question

Упражнение 17.7 1) Даю 30 баллов!

Answer 1

Ответ:

$b_2=9\ \ ,\ \ b_5=\dfrac{1}{3}\\\\b_2=b_1q=9\ \ \to \ \ \ b_1=\dfrac{b_2}{q}=\dfrac{9}{q}\\\\b_5=b_1q^4=(b_1q)\cdot q^3=b_2q^3=9q^3\ \ ,\ \ \ 9q^3=\dfrac{1}{3}\frac{x}{y} \ \ ,\ \ q^3=\dfrac{1}{27}\ \ ,\ \ \boxed {\ q=\dfrac{1}{3}<1\ }\\\\\\S=\dfrac{b_1}{1-q}\ \ ,\ \ \ b_1=\dfrac{9}{1/3}=27\\\\\\S=\dfrac{27}{1-\frac{1}{3}}=\dfrac{27}{2/3}=\dfrac{27\cdot 3}{2}=\dfrac{81}{2}=40,5\ \ ,\ \ \ \ \ \boxed{\ S=40,5\ }$