How do you find the equation for a circle with a center at (1,2) that passes through the point (-2,-1)?

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Answer 1 · 2016-01-04T22:19:33

If it passes thru $(-2,-1)$ , then use the distance formula to find the radius (r) ...

radius $r=sqrt[(1-(-2))^2+(2-(-1))^2]=sqrt(18)$

The general equation for a circle is:

$(x-h)^2+(y-k)^2=r^2$

where, center $=(h,k)=(1,2)$

Now, since we know the value of $h,k, and r$ ...

$(x-1)^2+(y-2)^2=(sqrt18)^2=18$

hope that helped

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