daca sunt in progresie geometrica,pun conditia ca nr din mijloc sa fie media geometrica a vecinilor
x+7=[tex] \sqrt{(5-x)(3x+11)} [/tex] |²
(x+7)²=(5-x)(3x+11)
x²+14x+49=15x+55-3x²-11x
x²+14x+49-15x-55+3x²+11x=0
4x²+10x-6=0 |:2
2x²+5x-3=0
Δ=25-4*2*(-3)=25+24=49
[tex]x_{1}= \frac{-5+7}{4} = \frac{1}{2} [/tex]
[tex]x_{2} = \frac{-5-7}{4} =-3[/tex]
