Question

(理)若(1+5x²)ⁿ的展開(kāi)式中各項(xiàng)系數(shù)之和是a_n,(2x³+5)ⁿ的展開(kāi)式中各項(xiàng)的二項(xiàng)式系數(shù)之和為b_n,則的值為

A.-               B.-              C.                D.

Answer 1

答案：(理)D  令x=1,得各項(xiàng)系數(shù)之和為a_n=6ⁿ,(2x³+5)ⁿ的展開(kāi)式中各項(xiàng)二項(xiàng)式系數(shù)之和為b_n=2ⁿ,

∴=.