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Chapter 7

Section 7.1: The Coordinate Plane

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Objective

Students plot and identifyordered pairs on a coordinate

plane

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Imagine the top surface of your deskstretching in in every direction

If it continued to spread,

it would go right throughyour neighbor.

..and then through the

classroom walls.

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..and through the school and the hills andthe mountains and out into space until itwent on forever and ever in every direction.

Then, you would have a plane.

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Inm

athem

atics, a plane is a flatsurface that goes on forever in

every direction.

In Algebra, we use theC O O R D I N A T E P L A N E

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Coordinate Plane cont.

Horizontal Number Line

The coordinateplane is divided bytwo number lines.

One is horizontal,like the number lineyou already know.

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Vertical Number Line

The other is vertical, with

up being in the positivedirection and down beingthe negative direction.

An example of this is athermometer

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Putting it together

Horizontal and Vertical Number Lines Together

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The coordinate plane isfilled with points . . .

An infinite number ofpoints

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Coordinate Plane: Identifying keyparts

Y-axis: Thevertical axis orline

X-Axis: Thehorizontal line

Origin:wherethe two

linesmeet

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Coordinates & Coordinate Pair

Coordinates

To study a point in the plane, weassign a set of numbers

This is an address and helps youget to the point starting at theorigin

It has an x value and a y value

Coordinates are always writtenwith the x value first and thenthe y value, a comma betweenthe two

Written like this x,y

Coordinate Pair

A pair of points written with

parenthese is a coordinatepair

(x,y)

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Consider the points (4,-2)

The first number tells you

how far to move along thex-axis

Remember to start atthe origin

Start at the origin

and count 4spaces to the right

1 2 3 4

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Consider the points (4,-2)

The second number orynumber tells you how farto move up or down.

Remember to start atthe origin

Start at the origin

and count 4spaces to the right

1 2 3 4

-1

-2

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(0,0)

This is point (0,0)

at the origin

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The two number linesdivide the plane into four

regions.

Quadrants are labeledwith Roman Numerals.

We call the regions

quadrants.

In Quadrant I, all values are

positive.

In Quadrant II, x-values are negative,

while y-values are positive.

In Quadrant III, x- and y-values

are both negative.

In Quadrant IV, x-values arepositive and y-values are

negative.

III

III IV-5 5

010-10

5

-5

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2,4

3,1

2, 3

5,2

Give the coordinates of each point:

Now whats thequadrant ofeach point?

III

IVIII