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# helphelp

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The center of the circle with equation $$x^2+y^2=-2x-10y-16$$ is the point (x,y) . What is x+y?

ant101  Mar 29, 2017
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Sorry Austin, I thought I was deleting my own incorrect answer.

I can't put it back easily. Sorry.

Your answer was mostly good but it did have an error in it.   :(

austinruffino  Mar 29, 2017
edited by Melody  Mar 29, 2017
edited by Melody  Mar 30, 2017
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The center of the circle with equation x^2+y^2=-2x-10y-16  is the point (x,y) . What is x+y?

The question is worded poorly. x and y are variables, not the centre of the circle.

I will call the centre (h,k).  These are teh latters most commonly used for this.

$$x^2+y^2=-2x-10y-16\\ x^2+2x\quad +y^2+10y\quad =-16\\ \text{Complete the 2 squares}\\ x^2+2x+1\quad +y^2+10y+25\quad =-16+26\\ (x+1)^2\quad +(y+5)^2\quad =10\\ centre\;\;is\;\;(-1,-5)\\ h+k=-1+-5=-6$$

Melody  Mar 29, 2017
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It's alright, and sorry about mixing up the signs!

austinruffino  Mar 30, 2017

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