f(x²-2x)≥f(3)
x²-2x≤3
x²-2x-3≤0
(x-3)(x+1)≤0
x-3≤0 且 x+1≥0
x≤3 且 x≥-1
x ∈(-3/4,0) ∪ [-1,3] = (-3/4,0)