Giải bài 3 trang 76 SGK giải tích nâng cao 12

Ta có:

${{7}^{-1}}.14=\dfrac{14}{7}=2 \\ \dfrac{4}{{{3}^{-2}}}={{4.3}^{2}}=4.9=36 \\ {{\left( \dfrac{4}{5} \right)}^{-2}}={{\left( \dfrac{5}{4} \right)}^{2}}=\dfrac{{{5}^{2}}}{{{4}^{2}}}=\dfrac{25}{16} \\ \dfrac{{{\left( -18 \right)}^{2}}.5}{{{15}^{2}}.3}=\dfrac{{{\left( {{2.3}^{2}} \right)}^{2}}.5}{{{\left( 3.5 \right)}^{2}}.3}=\dfrac{{{2}^{2}}{{.3}^{4}}.5}{{{3}^{3}}{{.5}^{2}}}=\dfrac{4.3}{5}=\dfrac{12}{5}$