My Math Forum Finding the center and radius of a circle?

 Algebra Pre-Algebra and Basic Algebra Math Forum

 May 16th, 2010, 11:28 AM #1 Newbie   Joined: May 2010 Posts: 1 Thanks: 0 Finding the center and radius of a circle? Hi, So I have the following equation: x^2-12x+84=y^2+16y and I am trying to solve for the center and radius of the circle. I have been able to reduce it to (x-6)^2 - (y-^2 = 16 but the problem is that the standard form of equation is (x - h)^2 + (y - k)^2 = r^2 not (x - h)^2 - (y - k)^2 = r^2. Any ideas on how to change - to a +?
 May 16th, 2010, 12:06 PM #2 Global Moderator     Joined: Oct 2008 From: London, Ontario, Canada - The Forest City Posts: 7,946 Thanks: 1137 Math Focus: Elementary mathematics and beyond Re: Finding the center and radius of a circle? Equation of a conic section: $Ax^2\,+\,Bxy\,+\,Cy^2\,+\,Dx\,+\,Ey\,+\,F\,=\,0$ If $A\,=\,C$ and $B\,=\,0$ the equation is a circle, but $A\,\ne\,C$. Reference: http://en.wikipedia.org/wiki/Conic_s...an_coordinates
 May 16th, 2010, 03:59 PM #3 Global Moderator   Joined: Dec 2006 Posts: 20,751 Thanks: 2135 The equation x² - 12x + 84 = y² + 16y reduces to (x - 6)² - (y + 8)² = -112. It's not a circle! Should y² have been -y²?
May 16th, 2010, 04:00 PM   #4
Global Moderator

Joined: May 2007

Posts: 6,770
Thanks: 700

Re: Finding the center and radius of a circle?

Quote:
 Originally Posted by thyrgle Hi, So I have the following equation: x^2-12x+84=y^2+16y and I am trying to solve for the center and radius of the circle. I have been able to reduce it to (x-6)^2 - (y-^2 = 16 but the problem is that the standard form of equation is (x - h)^2 + (y - k)^2 = r^2 not (x - h)^2 - (y - k)^2 = r^2. Any ideas on how to change - to a +?
You can't - you've got a hyperbola.

 May 16th, 2010, 04:10 PM #5 Global Moderator     Joined: Oct 2008 From: London, Ontario, Canada - The Forest City Posts: 7,946 Thanks: 1137 Math Focus: Elementary mathematics and beyond Re: Finding the center and radius of a circle? Delete, please.

 Thread Tools Display Modes Linear Mode

 Similar Threads Thread Thread Starter Forum Replies Last Post daveyf Probability and Statistics 8 April 25th, 2011 07:32 AM smog890 Algebra 3 October 4th, 2010 06:42 PM aschenbr.rach Calculus 1 March 7th, 2010 11:52 AM rune2402 Algebra 4 February 27th, 2008 05:21 PM Igo Calculus 1 December 31st, 1969 04:00 PM

 Contact - Home - Forums - Cryptocurrency Forum - Top