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Mathematics

If 34x = (81)-1 and (10)1y=0.0001(10)^{\dfrac{1}{y}} = 0.0001, find the value of 2-x × 16y.

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Answer

Given,

34x=(34)134x=344x=4x=44x=1.\Rightarrow 3^{4x} = (3^4)^{-1} \\[1em] \Rightarrow 3^{4x} = 3^{-4} \\[1em] \Rightarrow 4x = -4 \\[1em] \Rightarrow x = -\dfrac{4}{4} \\[1em] \Rightarrow x = -1.

Given,

(10)1y=0.0001(10)1y=1104(10)1y=1041y=4y=14.\Rightarrow (10)^{\dfrac{1}{y}} = 0.0001 \\[1em] \Rightarrow (10)^{\dfrac{1}{y}} = \dfrac{1}{10^4} \\[1em] \Rightarrow (10)^{\dfrac{1}{y}} = 10^{-4} \\[1em] \Rightarrow \dfrac{1}{y} = -4 \\[1em] \Rightarrow y = -\dfrac{1}{4}.

Substituting value of x and y in 2-x × 16y, we get :

2x×16y=2(1)×1614=21×(24)14=2×24×14=2×21=2×12=1.\Rightarrow 2^{-x} \times 16^y = 2^{-(-1)} \times 16^{-\dfrac{1}{4}} \\[1em] = 2^1 \times (2^4)^{-\dfrac{1}{4}} \\[1em] = 2 \times 2^{4 \times -\dfrac{1}{4}} \\[1em] = 2 \times 2^{-1} \\[1em] = 2 \times \dfrac{1}{2} \\[1em] = 1.

Hence, 2-x × 16y = 1.

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