Posted by **AKHLAQ** on Friday, April 8, 2011 at 1:18pm.

Given the co-ordinates (x,y) of a center of a circle and it's radius. determine whether a point lies inside the circle or outside the circle? Tell three formlaes which are used in this question?

- Math - geometry? -
**Writeacher**, Friday, April 8, 2011 at 1:34pm
Please type your __subject__ in the **School Subject** box. Any other words, __including obscure abbreviations__, are likely to delay responses from a teacher who knows that subject well.

- analytic geometry -
**MathMate**, Friday, April 8, 2011 at 1:59pm
The equation of a circle with given centre (x0,y0) and radius r is given by:

(x-x0)²+(y-y0)²=r²

implicitly, this equations makes use of the equation of distance between two points (x,y) and (x0,y0):

Distance = sqrt((x-x0)²+(y-y0)²)

If the distance from the centre is greater than r, then it is outside the circle. If the distance is less than r, then it is inside the circle.

I.e.

Point P1(x1,y1) is outside, on, or inside the circle if

(x1-x0)²+(y1-y0)²

is greater than, equal to, or less than

r².

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