Question

How would I write the equation of a circle with a center at (0, 0) and a radius of 5?

Answer 1

this is the fomrula for it (x-a)2 + (y-b)2 = r2

Answer 2

(h-0)^2 + (k-0)^2 = 25

Answer 3

I don't really understand still.

Answer 4

or x^2 + y^2 = 25

Answer 5

As an example, let us put some values to a, b and r and then expand it

Start with: (x-a)2 + (y-b)2 = r2

Set (for example) a=1, b=2, c=3: (x-1)2 + (y-2)2 = 32

Expand: x2 - 2x + 1 + y2 - 4y + 4 = 9

Gather like terms: x2 + y2 - 2x - 4y + 1 + 4 - 9 = 0
And we end up with this:

x2 + y2 - 2x - 4y - 4 = 0

Answer 6

What I meant was how were you able to determine what ab, b and c is from the information i provided?

Answer 7

a, b and c*

Answer 8

a is x1 b is y1

Answer 9

c is radious squared

Answer 10

oh okay, so for my problem x1=0 and y1=0? and c would be 25

Answer 11

Ok so the circle formula is (x-h)^2 + (y-k)^2 = r^2

The midpoint will be (h, k) with radius (r).

Answer 12

yeah exactly

Answer 13

listen to cosm also hes correct

Answer 14

alright that is very helpful thank you both

Answer 15

heres a link also for further halp with this http://www.mathsisfun.com/algebra/circle-equations.html

Answer 16

x^2+y^2=25

Answer 17

http://www.regentsprep.org/Regents/math/algtrig/ATC1/circlelesson.htm