Today's Class of 9A

So today we did the usual which is at the start of class check over the homework that was page 495 and the numbers were 14-32, expect you don't do 28 but add 37.

Afterwards we learn a new lesson which is called Equations of Circles.

And the formula is like this:

And where:

r= the radius

(h,k)= the center of the circle. The h stands for the x, while the k stands for the y.

x and y...well x and y are the same as always

So an example that Mrs. Saatkamp gave us was this...plus a graph to visualize better:

When you look at the formula not even checking the graph, you may say "Oh so the center is (h=-3, k=2)". But that's a completely wrong answer.

The real answer is; (3, -2). "Why?" you may ask, well its quite simple. OK, since its -h and -k that means that if a positive number like 3 = h, then its really -3 in the formula because it would be like this:

-(+3)= -3, since positive * negative = negative

While -2 would be just +2 in the formula since its:

-(-2)=+2, since negative*negative=positive

So in the end the center would be (3,-2) and not (3, 2) so be careful!!

Also if you can see that you really don't have the radius but to find that out you just have to find out the square root of 16 which is 4, therefore r=4. Now you have the center (3, -2) and the length of the radius which is 4!

The other example that was give to us is:

Example 2:

As you can see this is an incomplete form and cannot be used as an equation of circles. So first let's get the radius which is an easy task to do. First we add +9 to each side, therefore canceling the -9 and making 0+9=9. After just get the square root of 9 which would be 3. Moreover the length of the radius would be 3 then. Afterwards lets work in order to get the center. So lets look at that lonely