# Stuck on this conic question?

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#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?
0
6 years ago
#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?
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#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?
0
6 years ago
#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).
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#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!
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6 years ago
#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
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#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
0
6 years ago
#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?
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#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.
0
6 years ago
#10
(Original post by alex2100x)
First year undergrad. A level/gcse maths.
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#11
(Original post by TeeEm)
Maths
0
6 years ago
#12
(Original post by alex2100x)
Maths

o.k.

look at this reference on conics first

CONIC SECTION REFERENCE.pdf
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6 years ago
#13
(Original post by alex2100x)
Maths

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

your question is way above further maths
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