Notam 3x-1=a
x+3=b
9-x=c
cond ca a,b,c sa fie in progresie geometrica este ca b²=ac
(x+3)²=(3x-1)(9-x)
x²+6x+12=27x-3x²-9+x
x²+6x+12=-3x²+28x-9
x²+3x²+6x-28x+12+9=0
4x²-22x+21=0
Δ=484-336=148
x1=(22-2√37)/8=2(11-√37)/8=(11-√37)/4
x2=(22+2√37)/8=2(11+√37)/8=(11+√37)/4
