Analysis and Approaches for IBDP Maths Ebook 2 | Page 266

Your Practice Set – Analysis and Approaches for IBDP Mathematics
(g)
A
k
1 k
� � ln
k k�1
dAk
1 1 �( k�1)(1) �( k)(1)
�
� � �
2 2
d k k k � �
� ( k �1)
�
k �1
dAk
1 k �1�
1
d k k k �( k �1)
dA k
1 1
� � �
2
d k k k( k �1)
� � �
2 � 2 �
dA k�1
k
� � �
k
d k
2
k ( k �1) 2
k ( k �1)
dA �k�1�
k
�
k
2
d k k ( k �1)
d 1
A k
��
2
d k k ( k �1)
dA k
0
dk � for k � 1
Thus, A
k
is decreasing.
�
�
256
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