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# Stuck on this conic question? Watch

1. A conic has eccentricity e=0.7, a focus (5,3) and directrix y=2x7. Find the points of intersection of the conic with line y=3.
I'm really stuck on this, and have no idea even where to start.
Any help guys?
2. (Original post by alex2100x)
A conic has eccentricity e=0.7, a focus (5,3) and directrix y=2x7. Find the points of intersection of the conic with line y=3.
I'm really stuck on this, and have no idea even where to start.
Any help guys?
eccentricity less than 1 is an ellipse...do you know the definition of e in the locus of a conic?
3. (Original post by TeeEm)
eccentricity less than 1 is an ellipse...do you know the definition of e in the locus of a conic?
No I do not. I also don't understand the relevance of the directrix, my lecturer didn't even mention directrix in relation to ellipses only parabolas care to enlighten me?
4. (Original post by alex2100x)
No I do not. I also don't understand the relevance of the directrix, my lecturer didn't even mention directrix in relation to ellipses only parabolas care to enlighten me?
an ellipse is the locus of a point whose distance from a fixed point(focus) to that from a fixed line(directrix) remains constant (e).
5. (Original post by TeeEm)
an ellipse is the locus of a point whose distance from a fixed point(focus) to that from a fixed line(directrix) remains constant (e).
Never seen it defined that way only seen it defined as the sum of two distances from two foci remains constant. I will check over the question again and report back!
6. (Original post by alex2100x)
Never seen it defined that way only seen it defined as the sum of two distances from two foci remains constant. I will check over the question again and report back!
ALL CONIC SECTIONS are defined as a locus using focus and directrix where different values of e produce different conics

e.g.
e=0 circle
0<e<1 ellipse
e=1 parabola
e>1 hyperbola (special case e=√2 rectangular hyperbola)

... the sum of two distances from two foci remains constant...

is a consequence of the definition which can easily be proven using the general definition
7. (Original post by TeeEm)
ALL CONIC SECTIONS are defined as a locus using focus and directrix where different values of e produce different conics

e.g.
e=0 circle
0<e<1 ellipse
e=1 parabola
e>1 hyperbola (special case e=√2 rectangular hyperbola)

... the sum of two distances from two foci remains constant...

is a consequence of the definition which can easily be proven using the general definition
didn't even know this and now I can't do any of the questions sorry for wasting your time
8. (Original post by alex2100x)
didn't even know this and now I can't do any of the questions sorry for wasting your time
my time is not wasted ...
What course do you do and what prior knowledge do you have?
9. (Original post by TeeEm)
my time is not wasted ...
What course do you do and what prior knowledge do you have?
First year undergrad. A level/gcse maths.
10. (Original post by alex2100x)
First year undergrad. A level/gcse maths.
undergrad in what subject?
11. (Original post by TeeEm)
undergrad in what subject?
Maths
12. (Original post by alex2100x)
Maths

o.k.

look at this reference on conics first

CONIC SECTION REFERENCE.pdf
13. (Original post by alex2100x)
Maths
next look at the link

this is FP3 level standard, but it has full solutions.

your question is way above further maths

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