bn = b₁ * q^n-1; b₁ = bn / q^n-1
2. b₁ = 1,6 ; q = 2
a) b₃ = b₁* q² = 1,6 * 4 = 6,4
б) b₅ = b₁ * q⁴ = 1,6 * 16 = 25,6
в) b₇ = b₁ * q⁶ = 1,6 * 64 = 102,4
г) bk = b₁ * q^k-1
4. a) b₆ = 1/27, q = 1/3
b₁ = b₆ / q⁵ = 1/27 : 1/243 = 243/27 = 9
б) b₇ = 256, q = -2
b₁ = b₇ / q⁶ = 256 / (-2)⁶ = 256/64 = 4