1
The sum
1!(n-1)! 2!(n-2)!
1
is equal to:
1!(n-1)!
Answers
Answered by
1
Answer:
question is improper..........
Answered by
0
Answer:
In+2.(n−1)+3(n−2)+......n.1
⇒tr=r(n−r)
∴ ∑
r=1
n
tr=∑
r=1
n
r(n−r)
=∑
r=1
n
(nr−r
2
)
=n.
2
n(n+1)
−
6
n(n+1)(2n+1)
=
2
n
2
(n+1)
−
6
(n
2
+n)(2n+1)
=
2
n
3
+n
−(
6
2n
3
+3n
2
+n
)=
6
n
3
−3n
2
+2n
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