Răspuns:
Dam factor comun 3 la puterea x:
[tex] {3}^{x - 3} ( {3}^{3} + {3}^{2} + 3 + 1) = 40[/tex]
[tex] {3}^{x - 3} \times 40 = 40[/tex]
[tex] {3}^{x - 3} = 1[/tex]
[tex] {3}^{0} = 1[/tex]
[tex]x = 3 + 0 = 3[/tex]
