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Question 0501a
Sigma Notation
Method of Differences I
Question
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Find, in terms of
n
,
{n,}
n
,
∑
r
=
1
n
(
u
r
−
1
−
u
r
)
,
\sum_{r=1}^n \Big( u_{r-1} - u_{r} \Big),
r
=
1
∑
n
(
u
r
−
1
−
u
r
)
,
given that
u
0
=
2
,
{u_{0}=2,}
u
0
=
2
,
u
1
=
3
{u_{1}=3}
u
1
=
3
and
u
2
=
6.
{u_{2}=6.}
u
2
=
6.
Attempt
The answer is of the form
u
n
−
1
−
a
{u_{n-1} - a}
u
n
−
1
−
a
u
n
−
a
{u_{n} - a}
u
n
−
a
u
n
+
1
−
a
{u_{n+1} - a}
u
n
+
1
−
a
a
−
u
n
−
1
{a - u_{n-1}}
a
−
u
n
−
1
a
−
u
n
{a - u_{n}}
a
−
u
n
a
−
u
n
+
1
{a - u_{n+1}}
a
−
u
n
+
1
where
a
=
{a=}
a
=
Answer
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