progresie geometrica pentru numerele a , b , c daca b²= ac
( lgx)² = lg( x+1) ·[ 1/4 ·lg( x+1)]
4lg²x= lg²( x+1)
[ 2 lgx - lg( x+1)] · [ 2lgx + lg( x+1) ]=0
2lgx- lg( x+1) =0 2lgx= lg(x+1) lgx²=lg(x+1 ) x²=x+1
x² -x -1 =0 Δ=1+4=5 x₁ =( 1 -√5)/2 negativ , fals
x₂=( 1+√5)/2
2lgx+lg(x+1) =0
2lgx= - lg(x+1)
lgx² = lg( x+1) la puterea (-1) x² = 1/ ( x+1)
x²( x+1) =1 cu radacina x= 3/4
numarul total de radacini n=2
