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Mathematics

The 6th term from the end of the G.P. 8, 4, 2, ……, 11024\dfrac{1}{1024} is :

  1. 132\dfrac{1}{32}

  2. 116\dfrac{1}{16}

  3. 164\dfrac{1}{64}

  4. 1128\dfrac{1}{128}

G.P.

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Answer

G.P. : 8, 4, 2, ……, 11024\dfrac{1}{1024}.

a = 8

r = 48=12\dfrac{4}{8} = \dfrac{1}{2}

l = 11024\dfrac{1}{1024}.

We know that,

nth term from the end=lrn1{\text{nth term from the end}} = \dfrac{l}{r^{n - 1}}

Substitute values we get:

6th term from the end=lr61=11024(12)5=11024×321=132.\Rightarrow {\text{6th term from the end}} = \dfrac{l}{r^{6 - 1}} \\[1em] = \dfrac{\dfrac{1}{1024}}{\Big(\dfrac{1}{2}\Big)^{5}} \\[1em] = \dfrac{1}{1024} \times \dfrac{32}{1}\\[1em] = \dfrac{1}{32}.

Hence, the 6th term from the end is 132\dfrac{1}{32}.

Hence, option 1 is the correct option.

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