[tex]2^{x} + 2^{-x} = a[/tex]
[tex](2^{x} + 2^{-x})^{2} = a^{2}[/tex]
[tex](2^{x})^{2} + 2*2^{x}*2^{-x} + (2^{-x})^{2} = a^{2}[/tex]
[tex](2^{2})^{x} + 2^{1+x-x} + (2^2)^{-x} = a^{2}[/tex]
[tex](2^{2})^{x} + 2^{1} + (2^2)^{-x} = a^{2}[/tex]
[tex](2^{2})^{x} + (2^2)^{-x} = a^{2} - 2[/tex]
[tex]4^{x} + 4^{-x}[/tex]
[tex](2^{2})^{x} + (2^{2})^{-x}[/tex]
Como [tex](2^{2})^{x} + (2^2)^{-x} = a^{2} - 2[/tex]:
[tex]4^{x} + 4^{-x} =(2^{2})^{x} + (2^{2})^{-x} =a^{2} - 2[/tex]
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Resposta:
[tex]4^{x} + 4^{-x}=a^{2} - 2[/tex]