Question

3.如果的展开式中含有非零常数项，则正整数n的最小值为

A.10                                          B.6                              C.5                                     D.3

Answer 1

C

解析：T_r+1=C3^n－r(－2)^rx^2n－5r，∴2n－5r=0.

∴r=.∵r是整数，∴n最小是5.