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Mathematics

(5)5×(5)3(-5)^5 \times (-5)^{-3} is equal to:

  1. 15\dfrac{1}{5}

  2. 5

  3. -25

  4. 25

Exponents

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Answer

As we know, for any non-zero rational number a

an=1ana^{-n} = \dfrac{1}{a^n} and an=1ana^{n} = \dfrac{1}{a^{-n}}.

(5)5×(5)3=(5)5×(15)3=(5×5×5×5×5)×(1×1×15×5×5)=3125×(1125)=(3125×1125)=(3125125)=25(-5)^5 \times (-5)^{-3}\\[1em] = (-5)^5 \times \Big(\dfrac{-1}{5}\Big)^3\\[1em] = (-5 \times -5 \times -5 \times -5 \times -5) \times \Big(\dfrac{-1 \times -1 \times -1}{5 \times 5 \times 5}\Big)\\[1em] = -3125 \times \Big(\dfrac{-1}{125}\Big)\\[1em] = \Big(\dfrac{-3125 \times -1}{125}\Big)\\[1em] = \Big(\dfrac{3125}{125}\Big)\\[1em] = 25

Hence, option 4 is the correct option.

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