5.在 6 4(1 ) (1 )x y+ +的展开式中,记 m nx y项的系数 ( , )f m n,则
($3, 0) (2,1) (1, 2) (0, 3)f f f f+ + +=$ ( )
参考答案
C
2014_浙江卷 (数学)
5.在 6 4(1 ) (1 )x y+ +的展开式中,记 m nx y项的系数 ( , )f m n,则
($3, 0) (2,1) (1, 2) (0, 3)f f f f+ + +=$ ( )
C
【解答】
【解析】令$x y=$ ,由题意知 (3, 0) (2,1) (1, 2) (0, 3)f f f f+ + +即为 10(1 )x+
展开式中 3x 的系数,故 ($3, 0) (2,1) (1, 2) (0, 3)f f f f+ + += 710120C=$,故选C
【答案】C