Tínha) (frac{{ - 3}}{{28}}.frac{{ - 7}}{9})b) (frac{{{2^{25}}{{.49}^3}}}{{{{14}^8}{{.8}^4}}}) 

* Hướng dẫn giải

a) \(\frac{{ - 3}}{{28}}.\frac{{ - 7}}{9} = \frac{{1.1}}{{4.3}} = \frac{1}{{12}}\)

b) 

\(\begin{array}{l}
\frac{{{2^{25}}{{.49}^3}}}{{{{14}^8}{{.8}^4}}} = \frac{{{2^{25}}.{{({7^2})}^3}}}{{{2^8}{{.7}^8}.{{({2^3})}^4}}}\\
 = \frac{{{2^{25}}{{.7}^6}}}{{{2^{20}}{{.7}^8}}} = \frac{{{2^5}}}{{{7^2}}} = \frac{{32}}{{49}}
\end{array}\)