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Calculus/circle formulae

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Expert: - 10/12/2009


Question
Hey, I'm in first year calculus in university and it seems my prof expects us to know the xy formula of a circle. I know all about functions with x and y values but never circles.

one sample question would be:

Find an equation of the circle that has center (-5, -2) and passes through the origin.
(x -   )2 + (y -   )2 =


Can you please tell me how I would do this and what the components of this circle formula mean? How do you arrange this formula to translate and transform this function? I think the primary fuctions is x^2 + y^2 =1.


Thanks so much.

Answer
The equation of a circle is (x-x0)² + (y-y0)² = r² where the center is at (x0,y0)
and the radius is r.  The radius, in this case, is the distance from (-5,-2) to the origin.
That would make it √(5²+2²) = √(25+4) = √29.

Your equation should then be (x+5)² + (y+2)² = 29.

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