Question

нужно найти b1 и$\left \{ {{b3+b6=420} \atop {b4-b5+b6=315}} \right.$ q1

Answer 1

$b3 + b6 = b1 {q}^{2} + b1 {q}^{5} = \\ b1 {q}^{2} (1 + {q})(1 - q + {q}^{2} ) = 420$

$b4 - b5 + b6 = b {q}^{3} - b {q}^{4} + b {q}^{5} \\ b {q}^{3} (1 - q + {q}^{2} ) = 315$

2 делим на 1

q / (1+q) = 3/4

4q =3+3q

q = 3

b = 315 / ( 27 * 7) = 45 / 27 = 5/3