Răspuns:
x ∈ (0; +∞)
lg²x-2lg x-3=0 , x>0
Notam lg x = t
t²-2t-3=0
Δ = b²-4ac = 4+12 = 16
t1,2 = (-b±√Δ)/2a
t1 = (2+4)/2 = 3
t2 = (2-4)/2 = -1
lg x = 3 ⇒ x = 1000
lg x = -1 ⇒ x = 1/10
x1 = 1000
x2 = 1/10 (=0,1)
S = {1000; 1/10}
