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If 7=5+ 17(5+ )+ 172(5+2 )+ 173(5+3 )+ , then the value of is :
(4) 6
Arithmetico-geometric series: multiply by 17 and subtract.
S- S7=5+ 7+ 72+ 73+
67S=5+ 1/71-1/7=5+ 6
S=7 6=5+ 6
=6
Answer: (4)
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