4^x+ 4^(1-x) =5 ;
4^x+ (4^1)*(4^(-x)) =5;
4^x+ 4*1/(4^x) =5 ; * * * t =4^x ; t+4*1/t =5 * * *
(4^x)² - 5*(4^x) +4 =0 ; * * *
[4^x=1 ; 4^x =4.⇔ [x =0 ;x =1
