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avatar+4624 

For what value of c will the circle with equation x210x+y2+6y+c=0 have a radius of length 1?

 Feb 5, 2018

Best Answer 

 #1
avatar+37165 
0

X^2 -10x   + 25   +  y^2 + 6y   +   9   = -c   + 25 + 9

(x-5)^2  +  (y+3)^2  = -c  + 34           

 

-c+34 = 1

-c=-33

c = 33

 Feb 5, 2018
edited by Guest  Feb 5, 2018
edited by Guest  Feb 5, 2018
 #1
avatar+37165 
0
Best Answer

X^2 -10x   + 25   +  y^2 + 6y   +   9   = -c   + 25 + 9

(x-5)^2  +  (y+3)^2  = -c  + 34           

 

-c+34 = 1

-c=-33

c = 33

ElectricPavlov Feb 5, 2018
edited by Guest  Feb 5, 2018
edited by Guest  Feb 5, 2018
 #2
avatar+4624 
+1

Thanks, EP! Amazing!

 Feb 6, 2018
 #3
avatar+199 
+2

Completing the square gives us (x5)2+(y+3)2=34c . Since we want the radius to be 1, we must have 34c=12 . It follows that c=33.

 Feb 6, 2018

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