# Math

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The standard form of a circle is Ax^2+Cy^2+Dx+Ey+F=0.

Write the equation for the circle:
Center (1,2), point on the circle (-2,-1).

Okay, I've always put circles in the form (x-h)^2+(y-k)^2=0. I got this:
r^2=(x-1)^2+(y-2)^2
then I substitute the point to find the radius:
r^2=(-3)^2+(-3)^2
r^2=18
So the answer I got is
18=(x-1)^2+(y-2)^2.

...So what's standard form, and can I change it from my answer to that?

Thx

• Math -

expand and bring all terms to the left side.

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