Question

已知a=0.8^0.7，b=0.8^0.9，c=1.2^0.8，則a，b，c的大小關(guān)系是（　�。�

A．b＞a＞c

B．c＞a＞b

C．c＞b＞a

D．a(chǎn)＞b＞c

Answer 1

分析：考察指數(shù)函數(shù)y=0.8^x與y=1.2^x在R上單調(diào)性且與1相比較即可得出．

解答：解：考察指數(shù)函數(shù)y=0.8^x在R上單調(diào)遞減，∴1＞0.8^0.7＞0.8^0.9．
考察指數(shù)函數(shù)y=1.2^x在R上單調(diào)遞增，∴1.2^0.8＞1．
綜上可得：c＞a＞b．
故選B．

點(diǎn)評(píng)：熟練掌握指數(shù)函數(shù)的單調(diào)性是解題的關(guān)鍵．