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3 y + x = 12 y = 8 x + 1

neither parallel or perpendicular

3 y + 4 x = 12 6 y = 8 x + 1

6 x 9 y = 10 3 x + 2 y = 1

perpendicular

y = 2 3 x + 1 3 x + 2 y = 1

y = 3 4 x + 1 3 x + 4 y = 1

parallel

For the following exercises, find the x - and y- intercepts of each equation

f ( x ) = x + 2

g ( x ) = 2 x + 4

( 2 0 ) ; ( 0 , 4 )

h ( x ) = 3 x 5

k ( x ) = 5 x + 1

( 1 5 0 ) ; ( 0 , 1 )

2 x + 5 y = 20

7 x + 2 y = 56

( 8 0 ) ; ( 0 28 )

For the following exercises, use the descriptions of each pair of lines given below to find the slopes of Line 1 and Line 2. Is each pair of lines parallel, perpendicular, or neither?

  • Line 1: Passes through ( 0 , 6 ) and ( 3 , −24 )
  • Line 2: Passes through ( −1 , 19 ) and ( 8 , −71 )
  • Line 1: Passes through ( −8 , −55 ) and ( 10 , 89 )
  • Line 2: Passes through ( 9 , −44 ) and ( 4 , −14 )

Line 1 :   m = 8       Line 2 :   m = 6       Neither

  • Line 1: Passes through ( 2 , 3 ) and ( 4 , 1 )
  • Line 2: Passes through ( 6 , 3 ) and ( 8 , 5 )
  • Line 1: Passes through ( 1 , 7 ) and ( 5 , 5 )
  • Line 2: Passes through ( −1 , −3 ) and ( 1 , 1 )

Line 1 :   m = 1 2       Line 2 :   m = 2       Perpendicular

  • Line 1: Passes through ( 0 , 5 ) and ( 3 , 3 )
  • Line 2: Passes through ( 1 , −5 ) and ( 3 , −2 )
  • Line 1: Passes through ( 2 , 5 ) and ( 5 , −1 )
  • Line 2: Passes through ( −3 , 7 ) and ( 3 , −5 )

Line 1 :   m = 2       Line 2 :   m = 2       Parallel

Write an equation for a line parallel to f ( x ) = 5 x 3 and passing through the point ( 2 ,  – 12 ) .

Write an equation for a line parallel to g ( x ) = 3 x 1 and passing through the point ( 4 , 9 ) .

g ( x ) = 3 x 3

Write an equation for a line perpendicular to h ( t ) = 2 t + 4 and passing through the point ( - 4 ,  – 1 ) .

Write an equation for a line perpendicular to p ( t ) = 3 t + 4 and passing through the point ( 3 , 1 ) .

p ( t ) = 1 3 t + 2

Find the point at which the line f ( x ) = 2 x 1 intersects the line g ( x ) = x .

Find the point at which the line f ( x ) = 2 x + 5 intersects the line g ( x ) = 3 x 5.

( 2 , 1 )

Use algebra to find the point at which the line f ( x ) =   4 5 x   + 274 25 intersects the line h ( x ) = 9 4 x + 73 10 .

Use algebra to find the point at which the line f ( x ) = 7 4 x + 457 60 intersects the line g ( x ) = 4 3 x + 31 5 .

( 17 5 , 5 3 )

Graphical

For the following exercises, the given linear equation with its graph in [link] .

f ( x ) = x 1

f ( x ) = 2 x 1

F

f ( x ) = 1 2 x 1

f ( x ) = 2

C

f ( x ) = 2 + x

f ( x ) = 3 x + 2

A

For the following exercises, sketch a line with the given features.

An x -intercept of ( 4 ,  0 ) and y -intercept of ( 0 ,  –2 )

An x -intercept of ( 2 ,  0 ) and y -intercept of ( 0 ,  4 )

A y -intercept of ( 0 ,  7 ) and slope 3 2

A y -intercept of ( 0 ,  3 ) and slope 2 5

Passing through the points ( 6 ,  –2 ) and ( 6 ,  –6 )

Passing through the points ( 3 ,  –4 ) and ( 3 ,  0 )

For the following exercises, sketch the graph of each equation.

f ( x ) = 2 x 1

g ( x ) = 3 x + 2

h ( x ) = 1 3 x + 2

k ( x ) = 2 3 x 3

f ( t ) = 3 + 2 t

p ( t ) = 2 + 3 t

x = 3

x = 2

r ( x ) = 4

q ( x ) = 3

4 x = 9 y + 36

x 3 y 4 = 1

3 x 5 y = 15

3 x = 15

3 y = 12

If g ( x ) is the transformation of f ( x ) = x after a vertical compression by 3 4 , a shift right by 2, and a shift down by 4

  1. Write an equation for g ( x ) .
  2. What is the slope of this line?
  3. Find the y- intercept of this line.

  • g ( x ) = 0.75 x 5.5
  • 0.75
  • ( 0 , 5.5 )

If g ( x ) is the transformation of f ( x ) = x after a vertical compression by 1 3 , a shift left by 1, and a shift up by 3

  1. Write an equation for g ( x ) .
  2. What is the slope of this line?
  3. Find the y- intercept of this line.

For the following exercises,, write the equation of the line shown in the graph.

y = 3

x = 3

For the following exercises, find the point of intersection of each pair of lines if it exists. If it does not exist, indicate that there is no point of intersection.

y = 3 4 x + 1 3 x + 4 y = 12

no point of intersection

2 x 3 y = 12 5 y + x = 30

2 x = y 3 y + 4 x = 15

( 2 ,  7 )

x 2 y + 2 = 3 x y = 3

5 x + 3 y = 65 x y = 5

( 10 ,  –5 )

Extensions

Find the equation of the line parallel to the line g ( x ) = 0. 01 x + 2 .01 through the point ( 1 ,  2 ) .

Find the equation of the line perpendicular to the line g ( x ) = 0. 01 x +2 .01 through the point ( 1 ,  2 ) .

y = 100 x 98

For the following exercises, use the functions f ( x ) = 0. 1 x +200 and  g ( x ) = 20 x + 0.1.

Find the point of intersection of the lines f and g .

Where is f ( x ) greater than g ( x ) ? Where is g ( x ) greater than f ( x ) ?

x < 1999 201 x > 1999 201

Real-world applications

A car rental company offers two plans for renting a car.

  • Plan A: $30 per day and $0.18 per mile
  • Plan B: $50 per day with free unlimited mileage

How many miles would you need to drive for plan B to save you money?

A cell phone company offers two plans for minutes.

  • Plan A: $20 per month and $1 for every one hundred texts.
  • Plan B: $50 per month with free unlimited texts.

How many texts would you need to send per month for plan B to save you money?

Less than 3000 texts

A cell phone company offers two plans for minutes.

  • Plan A: $15 per month and $2 for every 300 texts.
  • Plan B: $25 per month and $0.50 for every 100 texts.

How many texts would you need to send per month for plan B to save you money?

Practice Key Terms 5

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Source:  OpenStax, Essential precalculus, part 1. OpenStax CNX. Aug 26, 2015 Download for free at http://legacy.cnx.org/content/col11871/1.1
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