Discuss how the radius can be drawn from the center to any point on the circle.
Stress that in a linear equation, no variables are squared. In the parabola equation only one variable is squared, while two are squared in the circle equation.
Ax+BY=C Stress that linear equations have exponents of 1 on both the x and the y. With parabolas, either the x or the y has an exponent of 2. With circles, both x and y terms are squared. Also with circles, the coefficients (or denominators) are the same for x 2 and y 2 (You will see in another lesson that that is not true for ellipses.)
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Conics, or conic sections, are the intersection of a plane with an infinite double cone. If that plane cuts both cones, it is a hyperbola. If it is parallel to the edge of the cone, you get a parabola. If neither is the case, it is an ellipse. The ellipse is also a circle if the plane is perpendicular to the altitude of the cone.