-4 5 -

3 1 2
分析:根據(jù)單項(xiàng)式系數(shù)、次數(shù)的定義來(lái)求解.單項(xiàng)式中數(shù)字因數(shù)叫做單項(xiàng)式的系數(shù),所有字母的指數(shù)和叫做這個(gè)單項(xiàng)式的次數(shù).
解答:根據(jù)單項(xiàng)式定義得:?jiǎn)雾?xiàng)式-2
2x
3y
2的系數(shù)為-4,次數(shù)為5;-

的系數(shù)為-

,次數(shù)為3;mn的系數(shù)為1,次數(shù)為2.
點(diǎn)評(píng):本題考查了單項(xiàng)式定義.確定單項(xiàng)式的系數(shù)和次數(shù)時(shí),把一個(gè)單項(xiàng)式分解成數(shù)字因數(shù)和字母因式的積,是找準(zhǔn)單項(xiàng)式的系數(shù)和次數(shù)的關(guān)鍵.注意π是數(shù)字,不是字母;系數(shù)是1或-1時(shí),不能忽略.