b3-b1=8;
b5-b1=80
b3 = b1*q²
b5 = b1*q⁴
b1*q² - b1 = b1(q² - 1) = 8
b1*q⁴ - b1 = b1(q⁴ - 1) = b1(q² - 1)(q² + 1) = 8(q² + 1) = 80
8(q² + 1) = 80
q² + 1 = 10
q² = 9
q₁₂ = +- 3
b1 = 1
q = 3 q = -3
b3-b1=8;
b5-b1=80
b3 = b1*q²
b5 = b1*q⁴
b1*q² - b1 = b1(q² - 1) = 8
b1*q⁴ - b1 = b1(q⁴ - 1) = b1(q² - 1)(q² + 1) = 8(q² + 1) = 80
8(q² + 1) = 80
q² + 1 = 10
q² = 9
q₁₂ = +- 3
b1 = 1
q = 3 q = -3