Algebra

 

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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