Răspuns:
[tex] {2}^{x} + {2}^{ - x} = \frac{5}{2} = > {2}^{x } + \frac{1}{ {2}^{x} } = \frac{5}{2} = > t + \frac{1}{t} = \frac{5}{2} [/tex]
ne folosim de formula
[tex] {a}^{ - n} = \frac{1}{ {a}^{n} } = > {2}^{ - x } = \frac{1}{ {2}^{x} } [/tex]
folosim substituția
[tex]t = {2}^{x} [/tex]
x= -1 , x2= 1
