3^(4х-1):3^(4х+1)=3^(-2)=1/9
3^(4x-1)+3^(4x+1) = 3^(4x-1) * ( 1+ 3^(4x+1)^3^(4x-1))= =3^(4x-1) *(1+3^(4x+1-4x+1))=3^(4x-1)*(1+3^2)=3^(4x-1)*10