# 11x1 t11 07 chord of contact (2010)

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• Chord of Contact

• Chord of Contact

y

x

2 4x ay

• Chord of Contact

y

x

2 4x ay

We know the coordinates

of an external point (T)

• Chord of Contact

y

x

2 4x ay

0 0,T x y

We know the coordinates

of an external point (T)

• Chord of Contact

y

x

2 4x ay

0 0,T x y

We know the coordinates

of an external point (T)

From this external point,

two tangents can be drawn

meeting the parabola at P

and Q.

• Chord of Contact

y

x

2 4x ay

2(2 , )Q aq aq

2(2 , )P ap ap

0 0,T x y

We know the coordinates

of an external point (T)

From this external point,

two tangents can be drawn

meeting the parabola at P

and Q.

• Chord of Contact

y

x

2 4x ay

2(2 , )Q aq aq

2(2 , )P ap ap

0 0,T x y

We know the coordinates

of an external point (T)

From this external point,

two tangents can be drawn

meeting the parabola at P

and Q.

• Chord of Contact

y

x

2 4x ay

2(2 , )Q aq aq

2(2 , )P ap ap

0 0,T x y

We know the coordinates

of an external point (T)

From this external point,

two tangents can be drawn

meeting the parabola at P

and Q.

The line joining these two

points is called the chord

of contact.

• Chord of Contact

y

x

2 4x ay

2(2 , )Q aq aq

2(2 , )P ap ap

0 0,T x y

We know the coordinates

of an external point (T)

From this external point,

two tangents can be drawn

meeting the parabola at P

and Q.

The line joining these two

points is called the chord

of contact.

• (1) Parametric approach

• (1) Parametric approach

1 Show that has equation 2 2PQ p q x y apq

• (1) Parametric approach

1 Show that has equation 2 2PQ p q x y apq

2

2 2

Show the two tangents have equations

0 and 0px y ap qx y aq

• (1) Parametric approach

1 Show that has equation 2 2PQ p q x y apq

2

2 2

Show the two tangents have equations

0 and 0px y ap qx y aq

3 Show that is the point ,T a p q apq

• (1) Parametric approach

1 Show that has equation 2 2PQ p q x y apq

2

2 2

Show the two tangents have equations

0 and 0px y ap qx y aq

3 Show that is the point ,T a p q apq

4 0 0But is ,T x y

• (1) Parametric approach

1 Show that has equation 2 2PQ p q x y apq

2

2 2

Show the two tangents have equations

0 and 0px y ap qx y aq

3 Show that is the point ,T a p q apq

4 0 0But is ,T x y

a

xqp

qpax

0

0

• (1) Parametric approach

1 Show that has equation 2 2PQ p q x y apq

2

2 2

Show the two tangents have equations

0 and 0px y ap qx y aq

3 Show that is the point ,T a p q apq

4 0 0But is ,T x y

a

xqp

qpax

0

0

apqy 0

• (1) Parametric approach

1 Show that has equation 2 2PQ p q x y apq

2

2 2

Show the two tangents have equations

0 and 0px y ap qx y aq

3 Show that is the point ,T a p q apq

4 0 0But is ,T x y

a

xqp

qpax

0

0

00 22 is yya

xxPQ

apqy 0

• (1) Parametric approach

1 Show that has equation 2 2PQ p q x y apq

2

2 2

Show the two tangents have equations

0 and 0px y ap qx y aq

3 Show that is the point ,T a p q apq

4 0 0But is ,T x y

a

xqp

qpax

0

0

00 22 is yya

xxPQ

Hence the chord of contact is yyaxx 00 2

apqy 0

• (1) Parametric approach

1 Show that has equation 2 2PQ p q x y apq

2

2 2

Show the two tangents have equations

0 and 0px y ap qx y aq

3 Show that is the point ,T a p q apq

4 0 0But is ,T x y

a

xqp

qpax

0

0

00 22 is yya

xxPQ

Hence the chord of contact is yyaxx 00 2

apqy 0

notice

similarity

to tangent

• (2) Cartesian approach

• (2) Cartesian approach

1 1 1Show that has equation 2PT xx a y y

• (2) Cartesian approach

1 1 1Show that has equation 2PT xx a y y

T lies on PT 1010 2 yyaxx

• (2) Cartesian approach

1 1 1Show that has equation 2PT xx a y y

T lies on PT 1010 2 yyaxx

yyaxxyxP 0011 2equation with line on the lies ,

• (2) Cartesian approach

1 1 1Show that has equation 2PT xx a y y

T lies on PT 1010 2 yyaxx

2 2 2Show that has equation 2QT xx a y y

yyaxxyxP 0011 2equation with line on the lies ,

• (2) Cartesian approach

1 1 1Show that has equation 2PT xx a y y

T lies on PT 1010 2 yyaxx

2 2 2Show that has equation 2QT xx a y y

T lies on QT 2020 2 yyaxx

yyaxxyxP 0011 2equation with line on the lies ,

• (2) Cartesian approach

1 1 1Show that has equation 2PT xx a y y

T lies on PT 1010 2 yyaxx

2 2 2Show that has equation 2QT xx a y y

T lies on QT 2020 2 yyaxx

yyaxxyxP 0011 2equation with line on the lies ,

yyaxxyxQ 0022 2equation with line on the lies ,

• (2) Cartesian approach

1 1 1Show that has equation 2PT xx a y y

T lies on PT 1010 2 yyaxx

2 2 2Show that has equation 2QT xx a y y

T lies on QT 2020 2 yyaxx

yyaxxyxP 0011 2equation with line on the lies ,

yyaxxyxQ 0022 2equation with line on the lies ,

Hence the chord of contact is yyaxx 00 2

• (2) Cartesian approach

1 1 1Show that has equation 2PT xx a y y

T lies on PT 1010 2 yyaxx

2 2 2Show that has equation 2QT xx a y y

T lies on QT 2020 2 yyaxx

yyaxxyxP 0011 2equation with line on the lies ,

yyaxxyxQ 0022 2equation with line on the lies ,

Hence the chord of contact is yyaxx 00 2

Exercise 9H; 1c, 2d, 3, 6, 8, 10, 14

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