MCQ
If $64^{-\frac{1}{3}}\Big(64^{\frac{1}{3}}-64^\frac{2}{3}\Big)$ then $5\sqrt[\text{n}]{64}=$
  • A
    $25$
  • B
    $\frac{1}{125}$
  • C
    $625$
  • D
    $\frac{1}{5}$

Answer

  1. $25$
    Solution:
    We have to find $5\sqrt[\text{n}]{64}$ provided $\sqrt{5^\text{n}}=125$
    So,
    $\sqrt{5^\text{n}}=125$
    $5^{\text{n}\times\frac{1}{2}}=5^3$
    $\frac{\text{n}}{2}=3$
    $\text{n}=3\times2$
    $\text{n}=6$
    Substitute $\text{n}=6$ in $5^{\sqrt[\text{n}]{64}}$ to get
    $5^{\sqrt[\text{n}]{64}}=5^{2^{6\times\frac{1}{6}}}$
    $=5\times5$
    $=25$
    Hence the value of $5^{\sqrt[\text{n}]{64}}$ is 25
    The correct choice is a.

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