21.
ОДЗ: x-1>0 2x-4>0
x>1 2x>4
x>2
В итоге x∈(2; +∞)
log₂ (x-1)² - log₂ (2x-4) > log₂ 2
log₂ {(x-1)² / (2x-4)} > log₂ 2
- + +
---------- 2 --------- 3 -------------
\\\\\\\\\ \\\\\\\\\\\\\\\\
x=4 + + + | +
x=2.5 - - + | +
x= 0 - - - | -
x∈(2; 3)U(3; +∞)
Ответ: (2; 3)U(3; +∞)