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Circle Geometry

  • Thread starter thomas49th
  • Start date
  • #1
655
0

Homework Statement




The circle C, with the centre at the point A, has equation x² + y² - 10x + 9 = 0

Find:

a) the co-ordinates of A,

b) the radius of C

Homework Equations



(x-a)² + (y-b)² = r²


The Attempt at a Solution



... not sure what to do really. any suggestions

thanks :)
 

Answers and Replies

  • #2
737
0
Once you do one of these, you'll know how to do them all. Try completing the square for both variables.
 
  • #3
655
0
(x²-5) -16
(y²)+9=0

so does this mean (5,0) is the co-ordinate.
is the radius sqrt(16-9) = sqrt(7)

???

thanks
 
  • #4
737
0
You have a x2 and a y2. How would you get it into the form (x-a)2 and (y-b)2?
 
  • #5
655
0
sorry im not sure :( did i complete the square correctly?
 
  • #6
Defennder
Homework Helper
2,591
5
It's sort of only a bit correct. The equation of a circle is [itex](x-x_0)^2 + (y-y_0)^2 = r^2[/itex], where [itex]x_0[/itex] and [itex]y_0[/itex] are the coordinates of the centre and r is the radius.

Complete the square for x^2 - 10x + 9 first, then substitute the resulting expression back into the question, and move the constant to the RHS. You'll get the equation of circle.
 
  • #7
655
0
Thanks!!! :)
 

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