【答案】
分析:本題中四個(gè)選項(xiàng)中A,B,C三個(gè)是指數(shù)型函數(shù),D選項(xiàng)中函數(shù)是冪函數(shù)類型的,依據(jù)相關(guān)的函數(shù)單調(diào)性驗(yàn)證那個(gè)判斷是正確的即可.
解答:解:對(duì)于選項(xiàng)A:考察函數(shù)y=1.7
x性質(zhì)知1.7
2.5<1.7
3,A不正確
對(duì)于選項(xiàng)B:考察函數(shù)y=0.8
x性質(zhì)知0.8
2>0.8
3,B不正確
對(duì)于選項(xiàng)C:考察函數(shù)y=π
x性質(zhì)知
,C不正確
對(duì)于選項(xiàng)D:考察函數(shù)y=X
0.3性質(zhì)知1.7
0.3>0.9
0.3,D正確
由上分析知,判斷正確的是D.
故應(yīng)選D.
點(diǎn)評(píng):本題的考點(diǎn)是指數(shù)函數(shù)單調(diào)性的應(yīng)用,考查用函數(shù)的單調(diào)性比較大小,用單調(diào)性比較大小是函數(shù)單調(diào)性的一個(gè)重要應(yīng)用.