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Evaluate $a^3 - \dfrac{1}{a^3}$ if $a - \dfrac{1}{a} = 0$.

 Jul 11, 2024
 #1
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First, let's zoom in and focus on the equation we are given. Let's square it. We get

\((a^2 - 2 + 1/a^2) = 0\)

 

This will achieve the equation

\(a^2 - 1/a^2 = -2\)

 

Next, let's focus on what we are trying to find. We know that

\(a^3 - 1/a^3 = ( a - 1/a) ( a^2 + 1 + 1/a^2)\)

 

WAIT! The first term in what we must find is 0!

That means our answer is just 0. 

 

So 0 is our answer!

 

Thanks! :)

 Jul 11, 2024

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