Tìm n biết: 8^7 + 8^7 + 8^7 + 8^7/3^7 + 3^7 + 3^7: 2^7 + — Không quảng cáo

Phương pháp giải

Rút gọn vế trái

Nếu a ^m = a ⁿ ( a khác 0, a khác 1) thì m = n

$\begin{array}{l}\frac{{{8^7} + {8^7} + {8^7} + {8^7}}}{{{3^7} + {3^7} + {3^7}}}:\frac{{{2^7} + {2^7}}}{{{6^7} + {6^7} + {6^7} + {6^7} + {6^7} + {6^7}}} = {2^n}\\ \Leftrightarrow \frac{{{{4.8}^7}}}{{{{3.3}^7}}}:\frac{{{{2.2}^7}}}{{{{6.6}^7}}} = {2^n}\\ \Leftrightarrow \frac{{{{4.8}^7}}}{{{3^8}}}:\frac{{{2^8}}}{{{6^8}}} = {2^n}\\ \Leftrightarrow \frac{{{{4.8}^7}}}{{{3^8}}}.\frac{{{6^8}}}{{{2^8}}} = {2^n}\\ \Leftrightarrow \frac{{{2^2}.{{({2^3})}^7}{{.6}^8}}}{{{{(3.2)}^8}}} = {2^n}\\ \Leftrightarrow \frac{{{2^2}{{.2}^{21}}{{.6}^8}}}{{{6^8}}} = {2^n}\\ \Leftrightarrow {2^{23}} = {2^n}\\ \Leftrightarrow 23 = n\end{array}$

Vậy n = 23