Coordinate Geometry: Straight Lines & Circles Straight lines

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Coordinate Geometry: Straight Lines & Circles

Straight lines

A. Some basic operations

(i) Entering an equation in ‘GRAPH’ mode

Example:

(ii) Zooming or changing the viewing window

- Axis ranges:

- Or use ‘ ZOOM ’ menu via [F2]

(iii) Deleting a function

Highlight the equation using cursor

Then use [F2] to delete and [F1] to confirm

(iv) Exploring the effect of gradient in

(a) ‘ GRAPH ’ mode

with

(b) ‘ DYNA ’ mode

with in increments of

Activity: Explore the effect of changing the variable in using the two modes above.

Question: Which calculator mode did you find gave you greatest insight into what was happening?

Why? Which do you think would students find most useful?

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B: Intersection of two lines

Example: Enter the following equations in ‘ GRAPH ’ mode

,

Question: Find the point of intersection of the two lines using G-SOLVE

[F5] function.

C: Intersection of Lines and Parabolas

Example:

Enter the following equations in ‘

GRAPH

’ mode

,

Note that when using G-SOLVE to find more than one point of intersection, enables you to move to different solutions.

Exercise:

Q1. Find the point(s) of intersection for the following pairs of functions

(i) and .

(ii) and

(iii) and

(iv) and

(v) and

Q2. The three lines , and form a triangle.

Find the coordinates of the vertices of the triangle.

Hint: You will need to select 2 of the three lines at a time using and

Q3. Change one coefficient of or so that

(a) there are two points of intersection and

(b) there is one point of intersection.

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Circles

A. ‘CONICS’ mode

(i) Using the equation form

( ) ( )

.

Enter the following values:

Using G-SOLVE [F5] function, find the centre and radius of the circle.

Activity: Complete the table below for your choice of values for :

( ) ( )

Centre

Question: Why does it state that ?

(ii) Using the equation form

Enter the following values:

Using G-SOLVE [F5] function, find the centre and radius of the circle.

Activity: Complete the table below for your choice of values for :

Question: Why does it state that ?

Centre

Radius

Radius

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B: ‘GRAPH’ mode

(i) Equations of circles

In ‘ GRAPH ’ mode equations have to be entered in the form

With some algebraic manipulation the equation of a circle with centre

( )

and radius can be written in the usual form as

( ) ( ) and then rearranged to give √ ( )

This has to be entered as two separate equations on the graphics calculator:

Note: Equations can be copied and pasted by highlighting the equation and then using the ‘CLIP’, ‘COPY’ and ‘PASTE’ operations:

(ii) Intersection of circles & lines

Example: Find the points where the line meets the circle

( ) ( )

and find the length of the chord that is formed.

Exercise:

Q1. Find the points of intersection

( ) ( )

and

( ) ( )

.

Q2. Find the point of intersection of and and describe the geometrical situation.

Q3. Find an equation of a circle that …

…has a radius of ;

…doesn’t cross either axis;

…passes through the origin;

…has as a diameter.

Q4. Find the equation of a circle with centre

( )

which has the point

( )

on its circumference.

Does the point

( )

lie on the circle?

Q5. For each equation either give the centre and radius of the circle or a reason why it is not a circle.

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Some Circles Activities:

Q1. Can you create the following diagrams on your graphics calculator?

Circles touching the origin Concentric circles

Straight line and circle 4 large and one small circle

Q2. Draw all the possible ways in which two circles can be arranged in relation to one another. Try to produce a diagram of each arrangement on your calculator and write down the equations of circles you used.

Q3. Window challenge

This is a photo of a window in a church building in

Stratford-on-Avon, Warwickshire.

Can you re-create the outline of it on your graphical calculator?

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