find radius and center of circle

thetomps

Junior Member
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Sep 26, 2005
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Find the center and radius of the circle given by the equation
x^2 + y^2 + 10x - 8y + 5 = 0

x^2+10+y^2-8y=5
x^2+10x+25+y^2-8y+16 = 5+25+16
(x+5)^2 + (y-4) = 46

center (5,-4) radius 6 ???
 
thetomps said:
x^2 + y^2 + 10x - 8y + 5 = 0
x^2 + 10 + y^2 - 8y = 5
The "10" should be a "10x" and the "=5" should be an "= -5", right?

thetomps said:
(x+5)^2 + (y-4) = 46
center (5,-4) radius 6 ???
Given (x - h)<sup>2</sup> + (y - k)<sup>2</sup> = r<sup>2</sup>, the center is at (h, k), not (-h, -k), and the radius is r, not... I don't know how you got "6" from "sqrt[46]"...?

Eliz.
 
opps sorry so would it be center (5, 4); radius 7 how do I find this radius?
 
thetomps said:
opps sorry so would it be center (5, 4)
No; the center is at (h, k), not (-h, k).

thetomps said:
radius 7 how do I find this radius?
I don't know how you got sqrt[46] equalling 7. Don't you?

Also, as noted previously, there is a sign error in your first step. Until that is corrected, it is unlikely that the value for the radius will be correct.

Eliz.
 
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