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Mathematics

Determine the 12th term of a G.P. whose 8th term is 192 and common ratio is 2.

AP GP

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Answer

Given, a8 = 192 and r = 2.

By formula, an = arn - 1.

⇒ a8 = a(2)(8 - 1)
⇒ 192 = a(2)7
⇒ a = 19227=192128=32.\dfrac{192}{2^7} = \dfrac{192}{128} = \dfrac{3}{2}.

12th term of the G.P. is a12,

a12=32(2)121a12=32×211a12=3×210a12=3×1024a12=3072.\Rightarrow a{12} = \dfrac{3}{2}(2)^{12 - 1} \\[1em] \Rightarrow a{12} = \dfrac{3}{2} \times 2^{11} \\[1em] \Rightarrow a{12} = 3 \times 2^{10} \\[1em] \Rightarrow a{12} = 3 \times 1024 \\[1em] \Rightarrow a_{12} = 3072.

Hence, the 12th term of the G.P. is 3072.

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