4 . The first two terms of an infinite geometric series are respectively , where k � 0 . u1
2
� and
( a ) Find the common ratio r , giving the answer in terms of k .
k u2 �3k � 4k
2 3
[ 2 ]
( b ) Show that when 1 �k � 1, the sum to infinity S � of the geometric series 2 exists . [ 3 ]
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