2*3^(x-6)+6*3^(x-4)=56
3^(x-6)*(2*1+6*3²)=56
3^(x-6)*(2+54)=56
3^(x-6)=1
3^(x-6)=3⁰
x-6=0
x=6
или по свойству степени:
3^(x-6)=3^x/3⁶=3^x/729
3^(x-4)=3^x/3⁴=3^x/81
3^x(2/729)+3^x*(6/81)=56
3^x*(2/729+6/81)=56
3^x*(2/729+54/729)=56
3^x*(56/729)=56
3^x=729. 729=81*9=3⁴ *3²=3⁶
3^x=3⁶
x=6