Let x and y be complex numbers. If x + y = 2 and xy = 5 - x^2 - y^2, then what is x^2 + y^2?
Let's first focus on the first equation given.
Since we know that (x+y)2=x2+2xy+y2, squaring both sides on the first equation, we get that
x2+2xy+y2=4
Reaaranging the second equation a bit, we find that
x2+xy+y2=5
Wait! These two equations are quite similar to each other. Subtracting the second equation from the first equation, we get that
x2+2xy+y2=4x2+1xy+y2=5 −
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xy=−1
Now, let's look at the second equation again. We know that
x2+xy+y2=5x2+y2=5−xyx2+y2=5−(−1)=6
So the answer is 6...i think
Thanks! :)