Mathematics · Oct / Nov 2023 · Paper 21 · Question 2
YMA01
As printed in the paper
The question as text
2. A sequence u1 , u2 , u3 , … is defined by u1 = 3 un+1 = 2 – 4 un
Read automatically from the paper; the printed page above is exact.
Show the answer and mark scheme
2(a)[3]
=
= −
4,
=
3
u
u
u
2
3
3
4
100
2
2(b)[2]
u
=
33
×
3
+
+ −
4
+
3
r
3
=
1
r
= −8
(a)
4
M1: Attempts to use the iteration formula seen at least once. E.g. Award for
u + =
2
−
=
...
1 1
3
May be implied by
either a correct value assigned to the correct term. Condone 23 as 0.67 for
2u
2
4
or a correct follow through value. So ifu = −
then
u =
2
−
or 8 would score the mark
23
2
3
3
−
It must be a correct method. Watch for correct values attached to the wrong term
4
4
4
does achieve 2
2
,
2
,
2
E.g
u
=
−
u
=
−
u
=
−
3 but it is M0. It is assigned to
3u
2
3
4
2
3
4
2
A1: Any correct value assigned to the correct term. Either
u =
(but condone as 0.67)
u = − or
3
2
3
2 ,
A1: All 3 values correct and labelled:
=
= − AND
4
u = . May be awarded from part (b)
3
u
u
2
3
3
4
(b)
M1: Establishes a correct method to find the sum of 100 terms.
Amongst other correct methods are;
2
33
×
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