2-3-11 please have hw out to correct.. equations with two variables lesson 8-2 p.391

2-3-11

Please have hw out to correct.

Equations with Two Variables

Lesson 8-2 p.391

Equations with Two Variables In the other chapters, we learned how

to solve equations like this: 5x + 3 = 2x +9

In this type of equation, there was only one kind of variable—”x”.

Now we will learn how to solve variables like: y = 2x + 3


y = 2x + 3

What do you notice about this equation?

Equations with Two Variables y = 2x + 3

What do you notice about this equation? Yes there are two kinds of variables—an x and a y.

We will find in this chapter that the solution to this type of equation is an ordered pair and if we graph the ordered pairs of the equation, we get a straight line when the points are connected.


We will also find that an equation like y = 2x + 3 can have many solutions, not just one, but it is the graph of the solutions that will be our answer.

Let’s start with one way to solve this type of problem. . .a t-table or t-chart


y = 2x + 3 One strategy is to make a table of

values or a t-table. It looks like this:

X Y

Equations with Two Variables y = 2x + 3

We begin by choosing any value we want for x. This may seem odd to you, but the reason will become apparent later.

I like to choose one positive number, one negative number and the number zero.

Equations with Two Variables y = 2x + 3 Let’s choose 1, 0 and -2

x y 1 Place the x values in 0 the chart. This reminds -2 us which numbers to

substitute for x.


y = 2x + 3 Then we substitute each

value one at a time and

x y solve for “y”

1 5 2(1) + 3 = 5

0

-2





1 5 2(1) + 3 = 5

0 3 2(0) + 3 = 3

-2





1 5 2(1) + 3 = 5

0 3 2(0) + 3 = 3

-2 -1 2(-2) + 3 = -1


The information in the t-table is a series of ordered pairs that when graphed on the coordinate plane, will result in a straight line like this


x y1 50 3-2 -1

First, plot point (1,5)


x y1 50 3-2 -1

First, plot point (1,5)Then plot point (0,3)


x y1 50 3-2 -1

First, plot point (1,5)Then plot point (0,3)Then plot point (-2,-1)


x y1 50 3-2 -1

First, plot point (1,5)Then plot point (0,3)Then plot point (-2,-1)

Finally draw a line that connects and goes through the points.


This is the graph of the equation:

y = 2x + 3

We will find that each equation has its own unique graph.

Try This

Make a t-table for the equation y = 3x -2 using the following values for x

x y 3 0 -1

Try This


x y 3 7 3(3) – 2 = 7 0 -1

Try This


x y 3 7 3(3) – 2 = 7 0 -2 3(0) – 2 = -2 -1

Try This


x y 3 7 3(3) – 2 = 7 0 -2 3(0) – 2 = -2 -1 -5 3(-1) – 2 = -5

Try This

x y

3 7

0 -2

-1 -5

Now graph the

Ordered pairs

Try This

x y

3 7

0 -2

-1 -5

One more Thing

Sometimes, an equation will be given as well as a sample ordered pair, and you will be asked “Is this a solution to the equation?”

For example, is (4,3) a solution to this equation: y = -2x + 2

Substitute the ordered pair in the solution: 3 = -2(4) + 2

In this case 3 = -8 + 2 or

3 = -6 is not true, so no it is not a solution.

Try This

Is (3,0) a solution to y = 2x – 6 0 = 6 – 6 0=0

Is (-2,5) a solution to y = -3x + 1 5 = 7

Try This

Is (3,0) a solution to y = 2x – 6 yes

Is (-2,5) a solution to y = -3x + 1 no

2-3-11 Agenda

PA#13:

Pp.394-395

#12-18 even, 20-30 even

2-3-11 please have hw out to correct.. equations with two variables lesson 8-2 p.391

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x values

equation y

type of equation

variablesx y1

kinds of variablesan

table of values

following values

time andx ysolve