Question

геометрическая прогрессия найти b1
b3=18
b5=162

Answer 1

{$b_n$}  - геометрическая прогрессия

$b_3=18$

$b_5=162$


$b_1-$ ?

$b_n=b_1*q^{n-1}$

$b_3=b_1*q^2$

$b_5=b_1*q^4$

$left { {{b_1*q^2=18} atop {b_1*q^4}=162} right.$

$left { {{b_1*q^2=18} atop {b_1*q^2*q^2}=162} right.$

$left { {{b_1*q^2=18} atop {18*q^2}=162} right.$

$left { {{b_1*q^2=18} atop {q^2}=9} right.$

$left { {{b_1= frac{18}{q^2} } atop {q^2}=9} right.$

$left { {{b_1= frac{18}{9} } atop {q^2}=9} right.$

$left { {{b_1= 2} } atop {q^2}=9} right.$

Ответ:  $2$