в геометрической прогрессии b9=1/4 , b11=1/8. найдите b1

b9 = b1 * q^(9-1) = b1 * q^8 = 1/4b11 = b1 * q^10 = 1/81/8 = (1/4) * q^10 / q^8q^2 = (1/8) / (1/4) = 1/2b1 = (1/4) / q^8 = (1/4) / (1/2)^4 = 2^4 / 2^2 = 2^2 = 4