4*(1/16)^x+15*(1/4)^x-4=0

4*(1/2)^4x+15*(1/2)^2x-4=0
произвожу замену  (1/2)^2x=t
ln((1/2)^2x)=ln t
2x*ln (1/2)=ln t
x=ln t/(2ln(1/2))
4t^2+15t-4=0
D=15^2+4*4*4=289
t1=-4 (не подходит),
 t2=0.25

x=ln0.25/(2*ln0.5)=1