MAT 125 – Applied Calculus 1.3 The Cartesian Coordinate System

MAT 125 – Applied Calculus1.3 The Cartesian Coordinate System

1.3 The Cartesian Coordinate System

2 Today’s Class

We will be learning the following concepts in Section 1.3: The Cartesian Coordinate System

The Distance Formula

The Equation of a Circle

We will be learning the following concepts in Section 1.4: Slope of a Line

Equations of Lines

Dr. Erickson


3

The Cartesian Coordinate System

At the beginning of the chapter we saw a one-to-one correspondence between the set of real numbers and the points on a straight line (one dimensional space).

Dr. Erickson

–4 –3 –2 –1 0 1 2 3 4


4


The Cartesian coordinate system extends this concept to a plane (two dimensional space) by adding a vertical axis.

Dr. Erickson

4

3

2

1

– 1

– 2

– 3

– 4

– 4 – 3 – 2 – 1 1 2 3 4


5


The horizontal line is called the x-axis, and the vertical line is called the y-axis.

x

y

Dr. Erickson

4

3

2

1

– 1

– 2

– 3

– 4

– 4 – 3 – 2 – 1 1 2 3 4


6


The point where these two lines intersect is called the origin.

y

x

Origin

Dr. Erickson

4

3

2

1

– 1

– 2

– 3

– 4

– 4 – 3 – 2 – 1 1 2 3 4


7


In the x-axis, positive numbers are to the right and negative numbers are to the left of the origin.

4

3

2

1

– 1

– 2

– 3

– 4

x

y

Positive DirectionNegative Direction

Dr. Erickson

4

3

2

1

– 1

– 2

– 3

– 4

– 4 – 3 – 2 – 1 1 2 3 4


8


In the y-axis, positive numbers are above and negative numbers are below the origin.

4

3

2

1

– 1

– 2

– 3

– 4

x

y

Pos

itive

Dir

ecti

onN

egat

ive

Dir

ecti

on

Dr. Erickson

4

3

2

1

– 1

– 2

– 3

– 4

– 4 – 3 – 2 – 1 1 2 3 4


9

4

3

2

1

– 1

– 2

– 3

– 4


A point in the plane can now be represented uniquely in this coordinate system by an ordered pair of numbers (x, y).

(– 2, 4)

(– 1, – 2)

(4, 3)

x

y

(3,–1)

Dr. Erickson

–4 –3 –2 –1 1 2 3 4


10


The axes divide the plane into four quadrants as shown below.

4

3

2

1

– 1

– 2

– 3

– 4

x

y

Quadrant I(+, +)

Quadrant II(–, +)

Quadrant IV(+, –)

Quadrant III(–, –)

Dr. Erickson

4

3

2

1

– 1

– 2

– 3

– 4

– 4 – 3 – 2 – 1 1 2 3 4


11 The Distance FormulaThe distance between any two points in the plane may be expressed in terms of their coordinates.

Distance formula

The distance d between two points P1(x1, y1) and P2(x2, y2) in the plane is given by

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2 2

2 1 2 1d x x y y


12

Example 1

Find the distance between the points (– 2, 1) and (10, 6).

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13

Example 2

Let P(x, y) denote a point lying on the circle with radius r and center C(h, k). Find a relationship between x and y.

Solution:

By definition in a circle, the distance between P(x, y) and C(h, k) is r. With distance formula we get

Squaring both sides gives

2 2x h y k r

2 2 2x h y k r

C(h, k)

h

kr

P(x, y)

y

x

Dr. Erickson


14 Equation of a Circle

An equation of a circle with center C(h, k) and radius r is given by

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2 2 2x h y k r


15

Example 3

Find an equation of the circle with radius 3 and center (–2, –4).

Find an equation of the circle centered at the origin and passing through the point (2, 3).

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16 Example 4

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17 Please continue on to Section 1.4

Dr. Erickson

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MAT 125 – Applied Calculus 1.3 The Cartesian Coordinate System