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Mathematics

Find the 6th term from the end of the list of numbers 3, -6, 12, -24, …. , 12288.

AP GP

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Answer

The given list of numbers 3, -6, 12, -24, …. , 12288 is a G.P. with last term = l = 12288 and the common ratio = r = -2.

By formula, nth term from end = l(1r)n1l\Big(\dfrac{1}{r}\Big)^{n - 1}

7th term from end =12288(12)61=12288(12)5=1228832=384.\text{7th term from end } = 12288\Big(-\dfrac{1}{2}\Big)^{6 - 1} \\[1em] = 12288\Big(-\dfrac{1}{2}\Big)^5 \\[1em] = -\dfrac{12288}{32} \\[1em] = -384.

Hence, the 6th term from end of the G.P. is -384.

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