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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?

 Dec 7, 2024
 #1
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+1

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    

______________________

xy=1

 

Now, let's look at the second equation again. We know that

x2+xy+y2=5x2+y2=5xyx2+y2=5(1)=6

 

So the answer is 6...i think

 

Thanks! :)

 Dec 8, 2024
edited by NotThatSmart  Dec 8, 2024

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