化简:4n+3×4n-1+32×4n-2+…+3n-1×4+3n.
化简:4n+3×4n-1+32×4n-2+…+3n-1×4+3n.
数学人气:482 ℃时间:2020-04-06 20:34:14
优质解答
设S
n=4
n+3×4
n-1+3
2×4
n-2+…+3
n-1×4+3
n,
则
Sn=+4n+3×4n−1+32×4n−2+…+3
n-2×4
2+3
n-1×4,
两式相减,得
Sn=
×4n+1−3n,
Sn=4n+1−3n+1.
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