Question

rația progresiei geometrice

Answer 1

$b_3=b_1*q^2$
$b_5=b_1*q^4$

$\left \{ {{b_1+b_1*q^2=5} \atop {b1*q^2+b_1*q^4=20}} \right.$

$\left \{ {{b_1(1+q^2)=5} \atop {b_1*q^2(1+q^2)=20}} \right.\Rightarrow \frac{b_1(1+q^2)}{b_1*q^2(1+q^2)} =\frac{5}{20}$

$\frac{\not{b}_1}{\not{b_1}*q^2}=\frac{1}{4} \rightarrow \frac{1}{q^2}= \frac{1}{4}$
$q^2=4 \Rightarrow q=\pm2$