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Official PYQ · 2018

GATE CS 2018 QGA-7 — General Aptitude

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 If pqr≠0pqr \ne 0 and p−x=1q,q−y=1r,r−z=1p,p^{-x}=\dfrac{1}{q},q^{-y}=\dfrac{1}{r},r^{-z}=\dfrac{1}{p}, what is the value of the product xyzxyz ?

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Answer: C

We are given the following three equations:

  1. p−x=1q  ⟹  p−x=q−1  ⟹  q=pxp^{-x} = \dfrac{1}{q} \implies p^{-x} = q^{-1} \implies q = p^x
  2. q−y=1r  ⟹  q−y=r−1  ⟹  r=qyq^{-y} = \dfrac{1}{r} \implies q^{-y} = r^{-1} \implies r = q^y
  3. r−z=1p  ⟹  r−z=p−1  ⟹  p=rzr^{-z} = \dfrac{1}{p} \implies r^{-z} = p^{-1} \implies p = r^z

Now, we can substitute the expression for qq from the first equation into the second equation:

r=(px)y=pxyr = (p^x)^y = p^{xy}

Next, substitute this expression for rr into the third equation:

p=(pxy)z=pxyzp = (p^{xy})^z = p^{xyz}

Since p=p1p = p^1, comparing the exponents on both sides gives:

xyz=1xyz = 1

Thus, the value of the product xyzxyz is 11.

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