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## sammy12 Group Title If xy = 6 and x^2 + y^2 = 16, then what is the value of (x + y)? 2 years ago 2 years ago

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1. ChrisV

X+y=5

2. sammy12

please can you explain

3. ChrisV

im trying to remember how to do this one sec

4. lazypig

$x ^{2}+y ^{2}+2xy =16+6\times2$ $\left( x +y \right)^{2}=28$ $x +y =\pm \sqrt{28}$

5. ChrisV

dunno how you came up with that but no way that works

6. sammy12

Thanks

7. ChrisV

its obvious the values of x and y are 2 and 3 but i cannot for the life of me remember how to explain it

8. ChrisV

so x+y=5

9. myininaya

$(x+y)^2=x^2+2xy+y^2=x^2+y^2+2(xy)=16+2(6)=16+12=28$ so we have $(x+y)^2=28 => x+y=\pm \sqrt{28}$

10. myininaya

so i agree with lazy :)