B4-b2=18 b5-b3=36 Найти b1

Решите задачу:

$\left \{ {{ b_{4} - b_{2} =18} \atop { b_{5} - b_{3} =36}} \right. \left \{ {{ b_{1}q^3- b_{1}q=18 } \atop {b_{1}q^4- b_{1}q^2=36}} \right. \left \{ {{b_{1}q(q^2-1)=18} \atop {b_{1}q^2( q^2-1)=36}} \right. \left \{ {{b_{1}= \frac{18}{q(q^2-1)} } \atop {b_{1}q^2( q^2-1)=36}} \right. \left \{ {{b_{1}= \frac{18}{q(q^2-1)} \atop {q= \frac{36}{18} }}$

$\left \{ {{b_{1}= \frac{18}{q(q^2-1)} \atop {q= \frac{36}{18} }} \left \{ {{b_{1}= \frac{18}{2(2^2-1)} \atop {q=2}} \right. \left \{ {{b_{1}= \frac{18}{6} \atop {q=2}} \right. b_{1}=3$