If the intersect curve of and are two lines

show that:

My idea is: joint the two equations:

then elimination one parameter: because is a plane, so

so let's Assume , then , take into in order to eliminate , we

get:

we know: it is a plane curve, and we know ,it replaces two plane lines if and only if :

where:

and I want to get the conclusion from : , But I failed, Help me