text: # equation of circle passing through (-1,-2) and concentric to the circle x2 +y2+3x+4y+1=0 is
  
  Arun
  25757 Points
  4 years ago
  Dear student
  
  concemtric circle means it is with same centre.
  hence centre of required circle = (-3/2, -4/2)
  
  also it passes throgh (-1, -2)
  hence radius= sqrt (1/4) = ½
  
  hence equation of circle
  (x+3/2)^2 + (y+2)^2= 1/4
  
  Navaneeth
  13 Points
  one year ago
  (-1,-2).  X^2+Y^2-3x+4Y-c=0
  X^2+Y^2-3X+4Y-C=0
  2G=3.         2F=4.    (from ax^2+by^2+2hxy+2gx+2fy+c=0
  G=-3/2.      F=2.        In which 2hxy=0 and c=0)
  -G=3/2.         -F=-2
  therefore (-3/2,--2)
  R=√(-3/2+2)^2+(0)^2   [ (x-h)^2+(y-k)^2=r^2 ]
  R=√(5/2)^2
  R=√25/4=5/2
  (r-h)^2+(y-k)^2=r^2
  (x-3/2)^2+(y+2)^2=25/4
  x^2-3x+9/4+y^2+4y+4=25/4
  x^2+y^2-3x+4y+9/4+4=25/4
  X^2+y^2-3x+4y+25/4=25/4
  x^2+y^2-3x+4y=0 is the equation of the circle
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