
Geometry Geometry Math Forum 
 LinkBack  Thread Tools  Display Modes 
September 1st, 2017, 10:49 AM  #1 
Newbie Joined: Aug 2017 From: Luweero, Uganda Posts: 4 Thanks: 0 Math Focus: differentiation  show that the equation x^2+y^2+4x+4=0 is a circle and determine its centre and radius
How can I Show that the equation x^2+y^2+4x+4=0 is a circle and determine its centre and radius?
Last edited by skipjack; September 1st, 2017 at 11:05 AM. 
September 1st, 2017, 10:53 AM  #2 
Math Team Joined: Dec 2013 From: Colombia Posts: 7,091 Thanks: 2360 Math Focus: Mainly analysis and algebra 
Perform a substitutions for $x$ and $y$ that result in the form $u^2 + v^2 = r^$. Are you sure your equation is correct? It looks like an odd sort of circle to me. 
September 1st, 2017, 11:06 AM  #3 
Global Moderator Joined: Dec 2006 Posts: 18,245 Thanks: 1439 
It's a single point. I've moved this problem to Geometry.

September 1st, 2017, 11:09 AM  #4 
Senior Member Joined: Mar 2015 From: New Jersey Posts: 1,194 Thanks: 91 
Irrelevant after moved. Delete button in Edit doesn't seem to work
Last edited by zylo; September 1st, 2017 at 11:11 AM. 
September 2nd, 2017, 05:30 AM  #5 
Math Team Joined: Jan 2015 From: Alabama Posts: 2,875 Thanks: 766 
Complete the square in x: $\displaystyle x^2+ 4x= x^2+ 4x+ 4 4= (x 2)^2 4$ (The graph of $\displaystyle x^2+ y^2+ 4x+ 4= 0$ is NOT a circle. It is the single point (2, 0).) 

Tags 
centre, circle, determine, equation, radius, show 
Thread Tools  
Display Modes  

Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
Determine Radius of Convergence, R  pjlloyd100  Calculus  3  November 11th, 2013 01:21 PM 
centre circle in 3D  andreaugust  Algebra  2  October 28th, 2013 10:29 AM 
Finding centre of a circle from a chord  berkeleybross  Algebra  4  December 8th, 2010 08:15 PM 
Finding equation of a circle without knowing its radius  aschenbr.rach  Calculus  1  March 7th, 2010 12:52 PM 
Centre and the radius of a circle  squeeze101  Algebra  3  November 21st, 2008 07:37 PM 