Question

设展开式的各项系数之和为A,而它的二项式系数之和为B,A+B=272,则n等于(    )

A.4                      B.5                    C.3                  D.16

Answer 1

答案：A

解析：令x=1,得A=4ⁿ,

又B=2ⁿ,∴4ⁿ+2ⁿ=272.∴(2ⁿ-16)(2ⁿ-17)=0.

∴2ⁿ=16,即n=4.