1) b2 = 3, b3 = 9/4
q = 9/4 : 3 = 9/4*1/3= 3/4
q = 3/4
b2 = b1*q
3 = b1*3/4
b1 = 3 : 3/4 = 3 * 4/3 = 4
b1 = 4
2) b1 = 3, q = 1/3
b6 = b1*q^5= 3*(1/3)^5= 1/81
b6= 1/81
3) 2, 1, ...
b1 = 2, q = 1:2 = 1/2
bn = b1*q^(n-1)
1/16 = 2 * (1/2)^(n-1)
2^-4 = 2* 2^(1-n)
2^-4 = 2^(2 - n)
-4 = 2 - n
n = 6
Ответ: b6 = 1/16