SWBAT classify a conic section by its equation.

How can we classify a conic section without graphing?

10 minutes

One of our main goals today will be to **classify conic sections in general form** (*Ax*^{2} + *Bxy* + *Cy*^{2} +*Dx* + *Ey* + *F* = 0) without graphing or doing any calculations. I want student to notice patterns and see trends. This is also building a foundation for tomorrow when we start looking at conic sections that have been rotated.

I give students this worksheet and have them work on #1-12 with their table group to classify each conic section. I explain that I want them to try to figure each one out without doing any calculations or graphing. As they are working I will **listen to the conjectures** that I am hearing and will write them on the board. Here is a list of a few that I heard in one of my classes.

- #3 is a circle because
*A*and*C*are integers. - #4 is a hyperbola because
*A*or*C*is has a negative coefficient. - #8 is a parabola because there is only one squared term.
- #11 is an ellipse because
*A*and*C*are positive.

10 minutes

I start our discussion by looking at the conjectures (shown below) and seeing what the class thinks of them.

- #3 is a circle because
*A*and*C*are integers. - #4 is a hyperbola because
*A*or*C*is has a negative coefficient. - #8 is a parabola because there is only one squared term.
- #11 is an ellipse because
*A*and*C*are different values.

The interesting part of the conjectures is that many of them will be true, but they **may not be specific enough to be a general rule**. When my students talked about *A* or *C* being negative in a hyperbola, a student asked what would happen if both were negative. I made a simple example (-2x^{2} – 2y^{2 }= 100) and had them think about what would happen.

After we went through all of the conjectures and came to some definite conclusions, I ask students about the** B value** and what conclusions we can make about that. At this point they notice that

30 minutes

After our discussion about the *B* value, I tell students that we will investigate this more in the coming days. I tell students that the rest of the worksheet is for homework and is a good summary of all of our work with conic sections so far.