# Thread: conic sections and their families

1. ## conic sections and their families

When does the generic equation of the 2nd degree not represent a conic section or does it always represent a conic section (unless it has no possible solutions in real numbers)?

The other topic I would like like to devote this thread to is families (or sometime called pencils) of conics.
$\displaystyle C_1 + \lambda C_2 = 0$ represents the zero sets of the family of conics passing through the intersection points of conics $\displaystyle c_1 and c_2$ please note that $\displaystyle \lambda$ is a parameter
and assumes all possible real values.

$\displaystyle C_1 + C_2 = 0$ is the same as the logical operation of this must satisfy both $\displaystyle C_1 AND C_2 = 0$.however there is an incongruity: suppose $\displaystyle C_1|_{(x_1,y_1)} = -1$ and $\displaystyle C_2|_{(x_1,y_1)} = 1$. this still satisfies the combined equation of the 2 conics.But $\displaystyle {(x_1,y_1)}$ does not belong to the zero set of either original conic .i.e. it does not satisfy either of the original conic equations.

Furthermore the generated shape will have all the points of both conics plus some extra.thus while the resulting equation is a general equation of the second degree it forms no recognizable conic.

Is my reasoning correct or have have really missed out a lot of logic?

I really would not mind if anyone had anything extra to add to this or any thoughts upon the posed topics even if they do not solve my questions.