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I need to rationalize the expression 1/(∛(3)+∛(2))

 Feb 3, 2017

Best Answer 

 #2
avatar+9665 
+5

\(\dfrac{1}{\sqrt[3]{3}+\sqrt[3]{2}}\\ =\dfrac{(\sqrt[3]{3})^2-\sqrt[3]{3\times 2}+(\sqrt[3]{2})^2}{3 + 2}\\ =\dfrac{\sqrt[3]{9}-\sqrt[3]{6}+\sqrt[3]{4}}{5}\)

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 Feb 3, 2017
 #1
avatar+23251 
+5

Since  a3 + b3  =  (a + b)(a2 - ab + b2)

Use  (a2 - ab + b2)  where  a = cuberoot(3)  and  b = cuberoot(2). 

 Feb 3, 2017
 #2
avatar+9665 
+5
Best Answer

\(\dfrac{1}{\sqrt[3]{3}+\sqrt[3]{2}}\\ =\dfrac{(\sqrt[3]{3})^2-\sqrt[3]{3\times 2}+(\sqrt[3]{2})^2}{3 + 2}\\ =\dfrac{\sqrt[3]{9}-\sqrt[3]{6}+\sqrt[3]{4}}{5}\)

MaxWong Feb 3, 2017
 #3
avatar+129839 
+5

1 / [3^(1/3) + 2^(1/3) ] 

 

We realize that the denominator can be made to be a sum of cubes if we multiply  numerator and denominator by  [3^(2/3) - 3^(1/3)*2^(1/3) + 2^(2/3) ]

 

[3^(2/3) - 3^(1/3)*2^(1/3) + 2^(2/3) ] / ( [3^(1/3) + 2^(1/3) ]  [3^(2/3) - 3^(1/3)*2^(1/3) + 2^(2/3) ] )

 

[3^(2/3) - 3^(1/3)*2^(1/3) + 2^(2/3) ] /  [ (3^(1/3))^3  + (2^(1/3))^3 ]  =

 

[ 3^(2/3) - 3^(1/3)*2^(1/3) + 2^(2/3) ] / 5  =

 

[3^(2/3) - 6^(1/3) + 2^(2/3) ] / 5  =

 

[ ∛9 - ∛6  +  ∛4 ]  / 5

 

 

cool cool cool

 Feb 3, 2017

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