Analysis and Approaches for IBDP Maths Ebook 1 | Page 80

Your Practice Set – Analysis and Approaches for IBDP Mathematics
27
Paper 2 Section A – Finding an unknown
coefficient with given a term in
Example
Solution
In the expansion of
value of k .
2 2 8
kx ( kx � 4) , the coefficient of the term in
10
x is 4354560. Find the
[6]
2 8
( kx � 4)
�8�
�8�
� ( kx ) � � �( kx ) (4) � � �( kx ) (4)
�1�
� 2�
2 8 2 7 1 2 6 2
8 (
2 )
8�r
(4)
r
kx
� �
� � � � �
�r
�
2 8�
( x ) r
(M1) for valid expansion
16 2r
� x �
�16 � 2r
� 8
r � 4, which is corresponding to the 5 th term (A1) for identifying the term
The 5 th �8 � 2 4 4
term � � �(
) (4)
4 kx
� �
(A1) for correct term
2 �8�
2 4 4 10
( kx ) � �( kx ) (4) � 4354560x
�4�
(M1) for setting the equation
5
17920k � 4354560
(A1) for correct equation
5
k � 243
k � 3
A1 N3
[6]
72
SE Production Limited