NDA2011MathematicsSequences and SeriesActual

Which term of the series 1 4 ,- 1 2 , 1, is -128 ?

Options

A9th
B10 th
C11 th
D12 th

Correct answer

B. 10 th

Step-by-step solution

Since that given series are in G.P Where first term = 1 4 , common ratio =-2 Let -128 is n th term array rlrl & & -128 & = 1 4 (-2)^ n-1 & & -128 4 & =(-2)^ n-1 & & (-2)^9 & =(-2)^ n-1 & n & =9+1=10^ th array

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