Circles

r-radius (1/2 diameter)

d-diameter (2 x radius)

A circle is the set of points in a plane at a fixed distance (radius) from a fixed point (center).

^ - To the power of

(h,k)- the center of the circle

*the radius of the circle is established by taking

the square root of the (r) of the formula given.

To graph a circle from a standard form equation (which is posted above),

you need to do the following:

Example

Graph the following circle: (x+2)+(y-1)=9

To graph this circle, all you have to do is to look at the formula.

To find the radius you must take the square root of 9,

because the radius in the equation is squared. r= 3

(from the center of the circle, go out 3 spaces to the right,

left, top, and bottom, and make 4 dots).

To find the center of the circle (h,k), you must once again look at the equation.

To make the equation be true, (x-h),

h is supposed to be negative,

and the only thing to make h= positive 2

is to add two negatives together. h= -2, or x= -2

To find k, use the same way you found h.

To make a negative (y-k), you must add a positive.

(y-1) h=1 or y=1

Answer: