Questions on Geometry: Circles and their properties answered by real tutors!

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Question 146344: Find the equation of a circle with radius 5 and centered at (3,-1).
a. x^2+y^2-9x+2y-15=0
b. x^2+y^2-6x+2y+15=0
c. x^2+y^2-6x+2y-15=0
d. Find the equation of a circle with radius 5 and centered at (3,-1). <BR> a. <IMG SRC=/cgi-bin/plot-formula.mpl?expression=x%5E2%2By%5E2-9x%2B2y-15=0&x=0003 ALIGN=MIDDLE ALT='x^2+y^2-9x+2y-15=0' BORDER=0 ><BR> b. <IMG SRC=/cgi-bin/plot-formula.mpl?expression=x%5E2%2By%5E2-6x%2B2y%2B15=0&x=0003 ALIGN=MIDDLE ALT='x^2+y^2-6x+2y+15=0' BORDER=0 ><BR> c. <IMG SRC=/cgi-bin/plot-formula.mpl?expression=x%5E2%2By%5E2-6x%2B2y-15=0&x=0003 ALIGN=MIDDLE ALT='x^2+y^2-6x+2y-15=0' BORDER=0 ><BR> d. x^2+y^2+6x-2y+15=0}}
e. nota
i have no idea where to start ... thank you for your help in advance
: Find the equation of a circle with radius 5 and centered at (3,-1).
a. x^2+y^2-9x+2y-15=0
b. x^2+y^2-6x+2y+15=0
c. x^2+y^2-6x+2y-15=0
d. Find the equation of a circle with radius 5 and centered at (3,-1). <BR> a. <IMG SRC=/cgi-bin/plot-formula.mpl?expression=x%5E2%2By%5E2-9x%2B2y-15=0&x=0003 ALIGN=MIDDLE ALT='x^2+y^2-9x+2y-15=0' BORDER=0 ><BR> b. <IMG SRC=/cgi-bin/plot-formula.mpl?expression=x%5E2%2By%5E2-6x%2B2y%2B15=0&x=0003 ALIGN=MIDDLE ALT='x^2+y^2-6x+2y+15=0' BORDER=0 ><BR> c. <IMG SRC=/cgi-bin/plot-formula.mpl?expression=x%5E2%2By%5E2-6x%2B2y-15=0&x=0003 ALIGN=MIDDLE ALT='x^2+y^2-6x+2y-15=0' BORDER=0 ><BR> d. x^2+y^2+6x-2y+15=0}}
e. nota
i have no idea where to start ... thank you for your help in advance

Answer by aswathytony(47) About Me  (Show Source):
You can put this solution on YOUR website!
equation of circle with centre (h,k) and radius r is ( x -h)^2 +(y-k)^2= r^2.
here centre (h,k) = (3, -1) , r =5.
substituting these values in the equation we get,
(x - 3)^2 + (y - (-1))^2 = 5^2
(x-3)^2 + ( y + 1)^2 = 25
x^2 -6x +9 + y^2 + 2y + 1 =25
x^2 + y^2 - 6x +2y+ 9+1 - 25 =0
x^2 + y^2 - 6x + 2y -15 = 0