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# Rationalisation

I have a doubt. How do you rationalize the following expression? $$\frac{1}{\sqrt[3]{2} + 1}$$

Note by Swapnil Das
2 years, 2 months ago

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Let cube root of 2 be x.

Then multiply above and below with (x^2 - x + 1).

You get the denominator as (x^3 + 1) = 3 a rational number. · 2 years, 2 months ago

Can you explain what is the motivation behind "Multiply with $$x^2 - x + 1$$?"

For another expression, how do we determine what to do?

E.g. how do you rationalize $$\frac{1}{ \sqrt{2} + \sqrt[3] { 3} }$$? Staff · 2 years, 2 months ago

Hello, please see the problem " Inspired by Swapnil Das". · 1 year, 12 months ago

I couldn't understand these solutions that are posted.Can you tell an easy method? Please · 1 year, 12 months ago

Doubt again. Why should we multiply the given expression? · 2 years, 2 months ago

he used this identity $\displaystyle{\left( { x }^{ 3 }+1 \right) =\left( x+1 \right) \left( { x }^{ 2 }-x+1 \right) }$ · 2 years, 2 months ago