5^(2x) - 4*5^x - 5 >= 0
5^x = t t > 0
t^2 - 4t - 5 >=0
D = 16 + 20 = 36 = 6^2
t12 = (4 +- 6)/2 = 5 -1
(t + 1)(t - 5) >=0
метод интервалов
+++++++++[-1] --------------- [5] ++++++++++
t ∈ (-∞, -1] U [5, +∞) t > 0
t∈ [5, +∞)
t >= 5
5^x >= 5
x >= 1
x ∈ [1, +∞)