Question

下列說法正確的是

1. A.
   單項(xiàng)式y(tǒng)的次數(shù)是0，系數(shù)也是0
2. B.
   單項(xiàng)式的系數(shù)是-5，次數(shù)是3
3. C.
   -5是一次單項(xiàng)式
4. D.
   單項(xiàng)式2πx²y的系數(shù)是2π，次數(shù)是3

Answer 1

D
分析：根據(jù)單項(xiàng)式系數(shù)和次數(shù)的概念解答即可，單項(xiàng)式中的數(shù)字因數(shù)是單項(xiàng)式的系數(shù)，單項(xiàng)式中所有字母的指數(shù)和叫單項(xiàng)式的次數(shù)．
解答：A、單項(xiàng)式y(tǒng)的次數(shù)是1，系數(shù)也是1；故A錯(cuò)誤．
B、單項(xiàng)式=，所以其系數(shù)是-，次數(shù)是3；故B錯(cuò)誤．
C、-5的系數(shù)是-5，次數(shù)是0，所以-5是0次單項(xiàng)式；故C錯(cuò)誤．
D、單項(xiàng)式2πx²y的系數(shù)是2π，次數(shù)是3；故D正確．
故選D．
點(diǎn)評(píng)：本題考查單項(xiàng)式系數(shù)和次數(shù)的概念，將單項(xiàng)式中的數(shù)字因數(shù)與字母準(zhǔn)確分離是解題的關(guān)鍵，注意π是數(shù)字，而不是字母．