B3 = b1*q^2 ==>
b1*q^2 = 64
b1*(1/2)^2 = 64
b1 = 64 / 0.25
b1 = 256
S7 = (b1*(1 - q^7))/(1 - q) = (256*(1 - (1/2)^7))/(1 - (1/2)) = 508
X⁶ - x⁴ - x² + 1 = (x⁶ - x²) - (x⁴ - 1) = x²(x⁴ - 1) - (x⁴ - 1) =
= (x⁴ - 1)(x² - 1) = (x² - 1)(x² + 1)(x² - 1) = (x - 1)(x + 1)(x² + 1)(x - 1)(x + 1) =
= (x - 1)²(x + 1)²(x² + 1)