Question

設(shè)a＞l，則log_0.2a、0.2^a、a^0.2的大小關(guān)系是（ ）
A．log_0.2a＜0.2^a＜a^0.2
B．log_0.2a＜a^0.2＜0.2^a
C．0.2^a＜log_0.2a＜a^0.2
D．0.2^a＜a^0.2＜log_0.2a

Answer 1

【答案】分析：要判斷a＞l時(shí)log_0.2a、0.2^a、a^0.2的大小首先要掌握指數(shù)函數(shù)、對(duì)數(shù)函數(shù)的單調(diào)性，利用指、對(duì)函數(shù)的單調(diào)性進(jìn)行比較即可．
解答：解：∵a＞l∴l(xiāng)og_0.2a＜log_0.21=0    0＜0.2^a＜0.2=1    a^0.2＞a=1
∴l(xiāng)og_0.2a＜0.2^a＜a^0.2
  故選A
點(diǎn)評(píng)：本題考查的是指數(shù)函數(shù)、對(duì)數(shù)函數(shù)單調(diào)性的應(yīng)用．能靈活運(yùn)用指數(shù)函數(shù)、對(duì)數(shù)函數(shù)的圖象及單調(diào)性來(lái)比較大�。�