SOLUTION: if x+y=10 and xy=21 then evaluate x^3+y^3

Question 989741: if x+y=10 and xy=21 then evaluate x^3+y^3
Answer by ikleyn(52802)   (Show Source): You can put this solution on YOUR website!
.
You have the system of two equations

.

Express y from the first equation   y = 10-x   and substitute it into the second equation. You will have

x*(10-x) = 21,

= .

Apply the quadratic formula to solve this quadratic equation. You will get

= 3,    = 7.

It means that the original system has the solutions

x = 3, y = 7       and
x = 7, y = 3.

Based on it, calculate    + .

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