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Ellipse Questions and Answers

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Further Maths – Conics

Ellipse
2 2 �� �� �
Tangent to 2 + 2 = � �, � � + =

2 2 ℎ �
Tangent to 2 + 2 = ℎ, � 2 + 2 =

2 2
Normal to 2 + 2 = � �, � � ��
− �� �
= −

2 2 2 2
Normal to 2 + 2 = ℎ, � ℎ
− �
= −

2
Foci ± , Directrices = ± = − =√ − 2

------------------------------------------------------------------------------------------------------------------------------

1. Find the foci and directrices for the following ellipses


2 2 2 2
a) + = b) + = c) + = .

2. Find the cartesian equations of the ellipses with the following properties;

a) Foci at ± , , directrices at = ±9.

b) Foci at ± , , directrices at = ± .

3. Find the equations of the tangents and normals at the point given
2 2
a) + = , b) + = ,− c) + = ,

4. Find the equations of the tangent and normal to the ellipse + = at the point

P(5cost, 2sint).

5. Find the equations of the tangents to the given ellipses at the specified points;
� �
a) x = 4cos�, y= 3sin� at � = . b) x = cos�, y = 2sin� at � = .

2 2
6. The tangents at the points , � and , � to the ellipse 2 + 2 = are

2
perpendicular. Show that = − 2 .

7. Show that the line = + is a tangent to the ellipse with equation 9 + = . Find the

equation of the corresponding normal to the ellipse.


8. The orbit of the (former) planet Pluto is an ellipse with major axis of length 1.18 x 1010 km. and
eccentricity . Calculate the length of the minor axis.
9. The orbit of a satellite is an ellipse of eccentricity with the centre of the Earth as one focus.
The Earth may be treated as a sphere of radius 6400 km. If the least height of the satellite above
the earth’s surface is 400 k , what is the greatest height?

2 2
10. The point P(acos�, bsin�) is on the ellipse 2 + 2 = . The foci are at the points S and T and
is the eccentricity of the ellipse. Show that | � − � | = �.

2 2
11. Show that if the line = + is tangent to the ellipse 2 + 2 = then + = .

2 2
12.* The tangent and normal to the ellipse 2 + 2 = at the point P(acos�, bsin�) meet the x-axis
at T and G respectively. C is the centre of the ellipse and Y is the foot of the perpendicular from
C to the tangent at P. Prove that (i) CG.CT = − , (ii) CY.GP = .

2 2
13.*The tangent at P(acos�, bsin�) to the ellipse 2 + 2 = cuts the y-axis at Q. The normal at P
is parallel to the li e joi i g Q to o e focus S’. If S is the other focus, show that PS is parallel to
the y-axis.

2 2
14.* For the ellipse 2 + 2 = a vertical line is drawn through the focus with positive x-coordinate
which intersects the ellipse at Q where Q has positive y coordinate. The normal at Q passes
through the lowest point of the minor axis of the ellipse. If is the eccentricity of the ellipse
show that + − = and hence find to 2 decimal places.

15.* Let be the perpendicular distance from the origin to the tangent at a point P on the ellipse
2 2
2 + 2 = . If � � are the two foci of the ellipse show that
2
�� − �� = − 2 .

2 2
16.* Find the largest possible distance of any normal to the ellipse 2 + 2 = from the origin
(excluding the normals at (± , .
Jan 27­10:47

Jan 27­10:49

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