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If x+y=9 and xy=18, what is the value of x^3+y^3?

 Jan 23, 2022
 #1
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If x+y=9 and xy=18, what is the value of x^3+y^3?    

 

You can solve for x and y the long way around,

but we can see intuitively that they are 6 and 3.  

 

so         x3 + y3  =  63 + 33  =  216 + 27  =  238  

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 Jan 23, 2022
 #2
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NO NO NO SCRATCH THAT  

 

216 + 27  =  243  

 

Darn, that's what comes of trying to do addition in my head.  

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Guest Jan 23, 2022

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