Question

ПРОГРЕССИЯ
b1+b4=27 И b2-b3+b4=18
НАЙТИ :b1-?g-?

Answer 1

b₁ + b₄ = 27                            b₂ - b₃ + b₄ = 18
b₁ + b₁ * q³ = 27                     b₁q - b₁q² + b₁q³ = 18
b₁(1 + q³) = 27                       b₁q(1 - q + q²) = 18

$\frac{b _{1}(1+ q^{3}) }{ b_{1}q(1-q+ q^{2} ) }= \frac{27}{18}\\\\ \frac{(1+q)(1-q+ q^{2}) }{q(1-q+ q^{2}) }= \frac{3}{2}\\\\ \frac{1+q}{q} = \frac{3}{2}\\\\3q=2+2q\\\\q=2\\\\\\ b_{1}= \frac{27}{1+ q^{3} }= \frac{27}{1+8} = \frac{27}{9} =3$