Cho F = 2. 6^7 + 6^8/ 2^5. (9^4. 2. 3^7 + 3^8) . Khẳng định nào sau đây đúng?

Đáp án đúng là: A

$F=\frac{{2.6}^7+6^8}{2^5.\left(9^4-{2.3}^7+3^8\right)}=\frac{6^7.\left(2+6\right)}{2^5.\left[{\left(3^2\right)}^4-{2.3}^7+3^8\right]}=\frac{6^7.8}{2^5.\left(3^8-{2.3}^7+3^8\right)}$.

$=\frac{6^7.8}{2^5.\left({2.3}^8-{2.3}^7\right)}=\frac{6^7.8}{2^5{\mathrm{.2.3}}^7.\left(3-1\right)}=\frac{6^7.8}{2^6{.3}^7.2}=\frac{6^7.8}{2^7{.3}^7}$.

$=\frac{6^7.8}{{\left(2.3\right)}^7}=\frac{6^7.8}{6^7}=\frac{8}{1}=8$.

Vậy ta chọn đáp án A.