# diameter of a circle

• June 6th 2007, 05:12 AM
Alexander
diameter of a circle
Suppose AB is the diameter of a circle, where A = (-1,-3) and B = (3,-2). The equation of the circle is?

4(x-1)^2 +4(y+5/2)^2 =17
• June 6th 2007, 06:52 AM
ThePerfectHacker
Quote:

Originally Posted by Alexander
Suppose AB is the diameter of a circle, where A = (-1,-3) and B = (3,-2). The equation of the circle is?

4(x-1)^2 +4(y+5/2)^2 =17

I will give you the steps. I will not do your homework for you.

1)Find the midpoint between $A(-1,-3) \mbox{ and }B(3,-2)$. Use the midpoint formula (see below).

2)The answer to #1 is the center of circle.

3)Find the length between $A(-1,-3)\mbox{ and }B(3,-2)$. Use the distance formula (see below).

4)The answer to #4 is diamter length, find half of it.

5)You know the center of circle and its radius. You can now describe its equation.

---
Midpoint formula: $\left(\frac{x_1+x_2}{2}, \frac{y_1+y_2}{2} \right)$

Distance formula: $\sqrt{(x_1-x_2)^2+(y_1-y_2)^2}$