9B Class Posting

Today we first corrected the HW from previous class: Page 495 # 14-32 + 37 all except 28

Then we continued to the new topic: Lesson 9-8

Equations of Cirles

Where:

• r is the length of the radius
• h and k are the coordinates of the center of the circle(h is the coordinate in x-axis and k the coordinate in the y-axis).

Example 1:

Graph:

In order to graph you first need to discover the center of the circle. To find it out its simple: the x is the number in parenthesis with x and the y is the number in the parenthesis with y. Although, you need to apply the signs. The answer isn't (3,2) but (3,-2) because of the signs: Since the be 3 is subtracting in the equation, the coordinate number is positive, and since 2 is adding in the equation, the coordinated number is negative, therefore -2. So the coordinated of the center of the circle is (3,-2).

Now that you have the center, you know where to start the radius. The find the length of the radius you just need to square root the number that is outside the parenthesis. In the example its 16 the number outside, so is 4. The length of the radius is 4.

Example 2:

State the Center and the radius for:

In this case you first need to add 9 to both sides. Then you just get the coordinates and the length. When you have or the coordinate will always be zero, because will be . There fore the answer for the center will be (0,2). To find the lenght of the radius just , which is 3. So the circle has the center of (0,2) and the lenght of the radius is 3.

Our HW is page 501 # 11,12,13 + 20-32 all

***In the HW don't forget to apply distance formula: