12х-25=7х+5
12х-7х=5+25
5х=30
х=6
Lg56 = lg7*2^3 = lg7 + lg2^3 = log2(7)/log2(10) + 3lg2 = log2(7)*lg2 + 3lg2 = ab+3b = b(a+3)
Решение
log₂² x - 4log₂ x + 3 = 0
ОДЗ: x > 0
log₂ x = t
t² - 4t + 3 = 0
t₁ = 1
t₂ = 3
1) log₂ x = 1
x = 2¹
x₁ = 2
2) log₂ x = 3
x = 2³
x₂ = 8