化简:4n+3×4n-1+32×4n-2+…+3n-1×4+3n.
问题描述:
化简:4n+3×4n-1+32×4n-2+…+3n-1×4+3n.
答
设Sn=4n+3×4n-1+32×4n-2+…+3n-1×4+3n,
则
Sn=4 3
+4n+3×4n−1+32×4n−2+…+3n-2×42+3n-1×4,4n+1 3
两式相减,得
Sn=1 3
×4n+1−3n,1 3
Sn=4n+1−3n+1.