4. Решите неравенство: a) log2(x - 1) ≤ log2(2x + 3); б) log1/3(2x + 1) > -1.

a) x - 1 ≤ 2x + 3 и x - 1 > 0 => -4 ≤ x и x > 1 => 1 < x.
б) 2x + 1 > 0 и 2x + 1 < (1/3)^(-1) = 3 => x > -1/2 и 2x < 2 => x > -1/2 и x < 1 => -1/2 < x < 1.