Cho 2x = 3. Tính A = 8x + 4x - 2.

$A = {8^x} + {4^{x - 2}} = {2^{x.3}} + \frac{{{2^{x.2}}}}{4^2} = {3^3} + \frac{{{3^2}}}{4^2} = \frac{{441}}{16}.$