[16^x] -6*[4^x]+5=0 ........
пусть 4^x= t, t>0
t²-6t+5=0
D= 36-20=16
t1= (6+4)/2= 5
t2= (6-4)/2= 1
1) 4^x=1
x1=0
2) 4^x=5
x2= log4(5)