## Equations and Graphs of Circles: looking for lessons, links

Complex numbers, rational functions, logarithms, sequences and series, matrix operations, etc.

### Equations and Graphs of Circles: looking for lessons, links

I just need some links and information regarding this. For some reason I just haven't been able to grasp the concept of math lately and I am on my last lesson to. :(

Anyway

4mase

Posts: 8
Joined: Wed Jan 14, 2009 6:56 pm

Try here.

stapel_eliz

Posts: 1803
Joined: Mon Dec 08, 2008 4:22 pm

### Re: Equations and Graphs of Circles: looking for lessons, links

michelleytelly

Posts: 1
Joined: Tue Apr 07, 2009 6:50 pm

### Re: Equations and Graphs of Circles: looking for lessons, links

An easy basic start to recognizing equations of circles is that they have both an X squared and a Y squared. However, when you start comparing this equation to other types of graphs ie parabolas,hyperbolas, etc. it can get tricky so thats just a basic start!

Heres an example of how to find points to graph on a circle:
x^2+2X+Y^2+14Y-31=0

first, subtract the 31 from both sides,
X^2+2X+Y^2+14Y=-31

then complete the squares for X and Y

X^2+2X+1+Y^2+14Y+49

add the 1 and 49 you calculated from completing the square to the -31

X^2+2X+1+Y^2+14Y+49=81

Then factor the squares of x and y into an equation

(X+1)2+(Y+7)2=81

you can now decipher the radius and the center point of your cirle. since r^2=81 r=9, and your center is (-1,-7) just the opposite values of your X and Y equations. once you plot your center point, you move up,down, left, and right the number of spaces the radius is. so in this case you would go up, down, left, and right nine spaces.

Hope i helped! =]
Amuselvrx3

Posts: 1
Joined: Sun Apr 12, 2009 8:50 pm

### Re: Equations and Graphs of Circles: looking for lessons, links

I found this site to be helpful:
http://www.analyzemath.com/CircleEq/CircleEq.html
good luck!!!
garner10

Posts: 1
Joined: Mon Apr 13, 2009 1:05 am