SOLUTION: If x + y = 7 and xy = 5, what is x^3 + y^3?

First let us make these equivalent transformations:

 =  =  + .

So you have this identity:

 =  + .

Now let us substitute the given values x + y = 7 and xy =5 into this identity. You will get

 =  + 3*5*7.

Hence, 

 =  - 3*5*7 = 343 - 105 = 238.