How do you write and equation for a circle with Center: (-4, 9) and radius: 12?

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Answer 1 · 2016-06-25T07:20:34

#x^2+y^2+8x-18y-47=0#

The equation of a circle with center at #(h,k)# and radius #r# is

#(x-h)^2+(y-k)^2=r^2# (this is equivalent to distance of a point on circumference from center being equal to radius).

Hence the equation of a circle with center at #(-4,9)# and radius #12# is

#(x-(-4))^2+(y-9)^2=12^2# or

#(x+4))^2+(y-9)^2=144# or

#x^2+8x+16+y^2-18y+81=144# or

#x^2+y^2+8x-18y+97-144=0# or

#x^2+y^2+8x-18y-47=0#