Question

(3 x 2 - 1 x ) 5 的展开式中常数项是______

(3 x 2 - 1 x ) 5 的展开式中常数项是______．

Answer 1

T
r+1
=
C
r5
(3
x
2
)
5-r
(-
1
x
)
r
=
(-1)
r
3
5-r
C
35
x
10-
5
2
r
当r=4时，该通项为常数项，常数项为（-1）
4
×3×C
5
4
=15
故答案为15