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If (0.064)×(0.4)7=(0.4)x×(0.0256)2, (0.064)×(0.4)^7=(0.4)^x×(0.0256)^2 ,(0.064)×(0.4)7=(0.4)x×(0.0256)2,​ then the value of x−1−1x−1\frac{x^
Question

If (0.064)×(0.4)7=(0.4)x×(0.0256)2, (0.064)×(0.4)^7=(0.4)^x×(0.0256)^2 ,​ then the value of x11x1\frac{x^{-1}-1}{x-1}​ is

A.

-1/2

B.

2

C.

-3

D.

-1/3

Correct option is A

Given:
(0.064)×(0.4)7=(0.4)x×(0.0256)2(0.064) × (0.4)^7 = (0.4)^x × (0.0256)^2​​
Formula Used:
Laws of indices: am×an=am+na^m × a^n = a^{m+n}​ and (am)n=am×n(a^m)^n = a^{m × n}​​
Solution:
Express all base numbers as powers of 0.4.
0.064=(0.4)30.064 = (0.4)^3​​
0.0256=(0.4)40.0256 = (0.4)^4​​
Substitute these into the original equation:
(0.4)3×(0.4)7=(0.4)x×((0.4)4)2(0.4)^3 × (0.4)^7 = (0.4)^x × ((0.4)^4)^2​​
Add exponents on the left and multiply on the right.
(0.4)3+7=(0.4)x×(0.4)8(0.4)^{3+7} = (0.4)^x × (0.4)^8​​
(0.4)10=(0.4)x+8(0.4)^{10} = (0.4)^{x+8}​​
Equating the powers since the bases are identical:
10 = x + 8
x = 2
Now, substitute x = 2 into the required expression x11x1.\frac{x^{-1} - 1}{x - 1}.​​
Expression = 21121=0.511=0.5=12\frac{2^{-1} - 1}{2 - 1} = \frac{0.5 - 1}{1} = -0.5 = -\frac{1}{2}​​
Final Answer
So the correct answer is (a)

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