# 11X1 T12 09 locus problems

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• Locus Problems

• Locus Problems(get rid of the ps and qs)

• Locus Problems(get rid of the ps and qs)

We find the locus of a point.

• Locus Problems(get rid of the ps and qs)

We find the locus of a point.

1 Find the coordinates of the point whose locus you are finding.

• Locus Problems(get rid of the ps and qs)

We find the locus of a point.

1

2

Find the coordinates of the point whose locus you are finding.

Look for the relationship between the x and y values (i.e. get rid of the parameters)

• Locus Problems(get rid of the ps and qs)

We find the locus of a point.

1

2

Find the coordinates of the point whose locus you are finding.

Look for the relationship between the x and y values (i.e. get rid of the parameters)

a) Type 1: already no parameter in the x or y value.

• Locus Problems(get rid of the ps and qs)

We find the locus of a point.

1

2

Find the coordinates of the point whose locus you are finding.

Look for the relationship between the x and y values (i.e. get rid of the parameters)

a) Type 1: already no parameter in the x or y value.e.g. (p + q, 3)

• Locus Problems(get rid of the ps and qs)

We find the locus of a point.

1

2

Find the coordinates of the point whose locus you are finding.

Look for the relationship between the x and y values (i.e. get rid of the parameters)

a) Type 1: already no parameter in the x or y value.e.g. (p + q, 3) locus is y = 3

• Locus Problems(get rid of the ps and qs)

We find the locus of a point.

1

2

Find the coordinates of the point whose locus you are finding.

Look for the relationship between the x and y values (i.e. get rid of the parameters)

a) Type 1: already no parameter in the x or y value.e.g. (p + q, 3) locus is y = 3

b) Type 2: obvious relationship between the values, usually only one parameter.

• Locus Problems(get rid of the ps and qs)

We find the locus of a point.

1

2

Find the coordinates of the point whose locus you are finding.

Look for the relationship between the x and y values (i.e. get rid of the parameters)

a) Type 1: already no parameter in the x or y value.e.g. (p + q, 3) locus is y = 3

b) Type 2: obvious relationship between the values, usually only one parameter. 1,6 e.g. 2 tt

• Locus Problems(get rid of the ps and qs)

We find the locus of a point.

1

2

Find the coordinates of the point whose locus you are finding.

Look for the relationship between the x and y values (i.e. get rid of the parameters)

a) Type 1: already no parameter in the x or y value.e.g. (p + q, 3) locus is y = 3

b) Type 2: obvious relationship between the values, usually only one parameter. 1,6 e.g. 2 tt

6

6xt

tx

• Locus Problems(get rid of the ps and qs)

We find the locus of a point.

1

2

Find the coordinates of the point whose locus you are finding.

Look for the relationship between the x and y values (i.e. get rid of the parameters)

a) Type 1: already no parameter in the x or y value.e.g. (p + q, 3) locus is y = 3

b) Type 2: obvious relationship between the values, usually only one parameter. 1,6 e.g. 2 tt

6

6xt

tx

136

12

2

xy

ty

• c) Type 3: not an obvious relationship between the values, use a previously proven relationship between the parameters.

• c) Type 3: not an obvious relationship between the values, use a previously proven relationship between the parameters. qpqp , e.g. 22Given that pq = 3

• c) Type 3: not an obvious relationship between the values, use a previously proven relationship between the parameters. qpqp , e.g. 22Given that pq = 3 pqqp

qpx

2222

• c) Type 3: not an obvious relationship between the values, use a previously proven relationship between the parameters. qpqp , e.g. 22Given that pq = 3 pqqp

qpx

2222

62 yx

• c) Type 3: not an obvious relationship between the values, use a previously proven relationship between the parameters. qpqp , e.g. 22Given that pq = 3 pqqp

qpx

2222

62 yx

2005 Extension 1 HSC Q4c)The points and lie on the parabolaThe equation of the normal to the parabola at P is and the equation of the normal at Q is given by

2,2 apapP 2,2 aqaqQ ayx 42 32 apappyx

32 aqaqqyx

• c) Type 3: not an obvious relationship between the values, use a previously proven relationship between the parameters. qpqp , e.g. 22Given that pq = 3 pqqp

qpx

2222

62 yx

2005 Extension 1 HSC Q4c)The points and lie on the parabolaThe equation of the normal to the parabola at P is and the equation of the normal at Q is given by

2,2 apapP 2,2 aqaqQ ayx 42 32 apappyx

32 aqaqqyx (i) Show that the normals at P and Q intersect at the point R whose

coordinates are 2, 22 qpqpaqpapq

• c) Type 3: not an obvious relationship between the values, use a previously proven relationship between the parameters. qpqp , e.g. 22Given that pq = 3 pqqp

qpx

2222

62 yx

2005 Extension 1 HSC Q4c)The points and lie on the parabolaThe equation of the normal to the parabola at P is and the equation of the normal at Q is given by

2,2 apapP 2,2 aqaqQ ayx 42 32 apappyx

32 aqaqqyx (i) Show that the normals at P and Q intersect at the point R whose

coordinates are 2, 22 qpqpaqpapq(ii) The equation of the chord PQ is . If PQ passes

through (0,a), show that pq = 1 apqxqpy

21

• (iii) Find the locus of R if PQ passes through (0,a)

• (iii) Find the locus of R if PQ passes through (0,a)

qpapqx

• (iii) Find the locus of R if PQ passes through (0,a)

qpapqx

axqp

qpax

• (iii) Find the locus of R if PQ passes through (0,a)

qpapqx

axqp

qpax

222 qpqpay

• (iii) Find the locus of R if PQ passes through (0,a)

qpapqx

axqp

qpax

222 qpqpay 22 pqqpay

• (iii) Find the locus of R if PQ passes through (0,a)

qpapqx

axqp

qpax

222 qpqpay 22 pqqpay

2122

axay

• (iii) Find the locus of R if PQ passes through (0,a)

qpapqx

axqp

qpax

222 qpqpay 22 pqqpay

2122

axay

aaxy 3

2

• 2004 Extension 1 HSC Q4b)The two points and are on the parabola 2,2 apapP 2,2 aqaqQ ayx 42

• 2004 Extension 1 HSC Q4b)The two points and are on the parabola 2,2 apapP 2,2 aqaqQ ayx 42

2attxy (i) The equation of the tangent to at an arbitrary point

on the parabola is Show that the tangents at the points P and Q meet at R, where R is the point

ayx 42 2,2 atat apqqpa ,

• 2004 Extension 1 HSC Q4b)The two points and are on the parabola 2,2 apapP 2,2 aqaqQ ayx 42

2attxy (i) The equation of the tangent to at an arbitrary point

on the parabola is Show that the tangents at the points P and Q meet at R, where R is the point

(ii) As P varies, the point Q is chosen so that is a right angle, where O is the origin.Find the locus of R.

POQ

ayx 42 2,2 atat apqqpa ,

• 2004 Extension 1 HSC Q4b)The two points and are on the parabola 2,2 apapP 2,2 aqaqQ ayx 42

2attxy (i) The equation of the tangent to at an arbitrary point

on the parabola is Show that the tangents at the points P and Q meet at R, where R is the point

(ii) As P varies, the point Q is chosen so that is a right angle, where O is the origin.Find the locus of R.

POQ

ayx 42 2,2 atat apqqpa ,

1 OQOP mm

• 2004 Extension 1 HSC Q4b)The two points and are on the parabola 2,2 apapP 2,2 aqaqQ ayx 42

2attxy (i) The equation of the tangent to at an arbitrary point

on the parabola is Show that the tangents at the points P and Q meet at R, where R is the point

(ii) As P varies, the point Q is chosen so that is a right angle, where O is the origin.Find the locus of R.

POQ

ayx 42 2,2 atat apqqpa ,

1 OQOP mm1

020

020 22

aqaq

apap

• 2004 Extension 1 HSC Q4b)The two points and are on the parabola 2,2 apapP 2,2 aqaqQ ayx 42

2attxy (i) The equation of the tangent to at an arbitrary point

on the parabola is Show that the tangents at the points P and Q meet at R, where R is the point

(ii) As P varies, the point Q is chosen so that is a right angle, where O is the origin.Find the locus of R.

POQ

ayx 42 2,2 atat apqqpa ,

1 OQOP mm1

020

020 22

aqaq

apap

pqaqap 222 4

• 2004 Extension 1 HSC Q4b)The two points and are on the parabola 2,2 apapP 2,2 aqaqQ ayx 42

2attxy (i) The equation of the tangent to at an arbitrary point

on the parabola is Show that the tangents at the points P and Q meet at R, where R is the point

(ii) As P varies, the point Q is chosen so that is a right angle, where O is the origin.Find the locus of R.

POQ

ayx 42 2,2 atat apqqpa ,

1 OQOP mm1

020

020 22

aqaq

apap

pqaqap 222 44pq

• 2004 Extension 1 HSC Q4b)The two points and are on the parabola 2,2 apapP 2,2 aqaqQ ayx 42

2attxy (i) The equation of the tangent to at an arbitrary point

on the parabola is Show that the tangents at the points P and Q meet at R, where R is the point

(ii) As P varies, the point Q is chosen so that is a right angle, where O is the origin.Find the locus of R.

POQ

ayx 42 2,2 atat apqqpa ,

1 OQOP mm1

020

020 22

aqaq

apap

pqaqap 222 44pq

apqy

• 2004 Extension 1 HSC Q4b)The two points and are on the parabola 2,2 apapP 2,2 aqaqQ ayx 42

2attxy (i) The equation of the tangent to at an arbitrary point

on the parabola is Show that the tangents at the points P and Q meet at R, where R is the point

(ii) As P varies, the point Q is chosen so that is a right angle, where O is the origin.Find the locus of R.

POQ

ayx 42 2,2 atat apqqpa ,

1 OQOP mm1

020

020 22

aqaq

apap

pqaqap 222 44pq

apqy ay 4

• 2004 Extension 1 HSC Q4b)The two points and are on the parabola 2,2 apapP 2,2 aqaqQ ayx 42

2attxy (i) The equation of the tangent to at an arbitrary point

on the parabola is Show that the tangents at the points P and Q meet at R, where R is the point

(ii) As P varies, the point Q is chosen so that is a right angle, where O is the origin.Find the locus of R.

POQ

ayx 42 2,2 atat apqqpa ,

1 OQOP mm1

020

020 22

aqaq

apap

pqaqap 222 44pq

apqy ay 4

Exercise 9J; oddsup to 23

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