Cho các số thực dương a, b, c thỏa mãn a^log7=27
Phát biểu | Đúng | Sai |
\(\sqrt[3]{{{a^{{{\left( {{{\log }_3}7} \right)}^2}}}}} = 14\) | ¡ | ¤ |
\({c^{{{\left( {{{\log }_{11}}25} \right)}^2}}} = 5\) | ¤ | ¡ |
\(\sqrt[3]{{{a^{{{\left( {{{\log }_3}7} \right)}^2}}}}} + \sqrt {{b^{{{\left( {{{\log }_7}11} \right)}^2}}}} + {c^{{{\left( {{{\log }_{11}}25} \right)}^2}}} = 23\) | ¤ | ¡ |
Giải thích
\(\sqrt[3]{{{a^{{{\left( {{{\log }_3}7} \right)}^2}}}}} = \sqrt[3]{{{{\left( {{a^{{{\log }_3}7}}} \right)}^{{{\log }_3}7}}}} = \sqrt[3]{{{{27}^{{{\log }_3}7}}}} = \sqrt[3]{{{{\left( {{3^{{{\log }_3}7}}} \right)}^3}}} = 7\)
\(\sqrt {{b^{{{\left( {{{\log }_7}11} \right)}^2}}}} = \sqrt {{{\left( {{b^{{{\log }_7}11}}} \right)}^{{{\log }_7}11}}} = \sqrt {{{49}^{{{\log }_7}11}}} = \sqrt {{{\left( {{7^{{{\log }_7}11}}} \right)}^2}} = 11.\)
\({c^{{{\left( {{{\log }_{11}}25} \right)}^2}}} = {\left( {{c^{{{\log }_{11}}25}}} \right)^{{{\log }_{11}}25}} = {(\sqrt {11} )^{{{\log }_{11}}25}} = \sqrt {{{11}^{{{\log }_{11}}25}}} = \sqrt {25} = 5\)
Vậy \(\sqrt[3]{{{a^{{{\left( {{{\log }_3}7} \right)}^2}}}}} + \sqrt {{b^{{{\left( {{{\log }_7}11} \right)}^2}}}} + {c^{{{\left( {{{\log }_{11}}25} \right)}^2}}} = 7 + 11 + 5 = 23\).