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(1)计算:C33+C43+C53+…+C103(2)证明:Ank+kAnk-1=An+1k.
题目详情
(1)计算:C33+C43+C53+…+C103
(2)证明:Ank+kAnk-1=An+1k.
(2)证明:Ank+kAnk-1=An+1k.
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答案和解析
(1)∵Cmn+Cm-1n=Cmn+1,
∴原式=C44+C43+C53+…+C103
=C54+C53+C63+…+C103
=C64+C63+C73+…+C103
=…
=C104+C103
=C114
=330
(2)证明:∵
=
∴左边=
+k
=
=
=An+1k=右边
∴原式=C44+C43+C53+…+C103
=C54+C53+C63+…+C103
=C64+C63+C73+…+C103
=…
=C104+C103
=C114
=330
(2)证明:∵
A | n m |
n! |
(n−m)! |
∴左边=
n! |
(n−k)! |
n! |
(n−k+1)! |
=
n![(n−k+1)+k] |
(n−k+1)! |
=
(n+1)! |
(n−k+1)! |
=An+1k=右边
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