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Find the equation of the line parallel to 5 x = 7 + y and passing through the point ( −1 , −2 ) .

y = 5 x + 3

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Finding the equation of a line perpendicular to a given line passing through a given point

Find the equation of the line perpendicular to 5 x 3 y + 4 = 0 ( 4 , 1 ) .

The first step is to write the equation in slope-intercept form.

5 x 3 y + 4 = 0 −3 y = −5 x 4 y = 5 3 x + 4 3

We see that the slope is m = 5 3 . This means that the slope of the line perpendicular to the given line is the negative reciprocal, or 3 5 . Next, we use the point-slope formula with this new slope and the given point.

y 1 = 3 5 ( x ( −4 ) ) y 1 = 3 5 x 12 5 y = 3 5 x 12 5 + 5 5 y = 3 5 x 7 5
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Key concepts

  • We can solve linear equations in one variable in the form a x + b = 0 using standard algebraic properties. See [link] and [link] .
  • A rational expression is a quotient of two polynomials. We use the LCD to clear the fractions from an equation. See [link] and [link] .
  • All solutions to a rational equation should be verified within the original equation to avoid an undefined term, or zero in the denominator. See [link] and [link] .
  • Given two points, we can find the slope of a line using the slope formula. See [link] .
  • We can identify the slope and y -intercept of an equation in slope-intercept form. See [link] .
  • We can find the equation of a line given the slope and a point. See [link] .
  • We can also find the equation of a line given two points. Find the slope and use the point-slope formula. See [link] .
  • The standard form of a line has no fractions. See [link] .
  • Horizontal lines have a slope of zero and are defined as y = c , where c is a constant.
  • Vertical lines have an undefined slope (zero in the denominator), and are defined as x = c , where c is a constant. See [link] .
  • Parallel lines have the same slope and different y- intercepts. See [link] .
  • Perpendicular lines have slopes that are negative reciprocals of each other unless one is horizontal and the other is vertical. See [link] .

Section exercises

Verbal

What does it mean when we say that two lines are parallel?

It means they have the same slope.

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What is the relationship between the slopes of perpendicular lines (assuming neither is horizontal nor vertical)?

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How do we recognize when an equation, for example y = 4 x + 3 , will be a straight line (linear) when graphed?

The exponent of the x variable is 1. It is called a first-degree equation.

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What does it mean when we say that a linear equation is inconsistent?

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When solving the following equation:

2 x 5 = 4 x + 1

explain why we must exclude x = 5 and x = −1 as possible solutions from the solution set.

If we insert either value into the equation, they make an expression in the equation undefined (zero in the denominator).

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Algebraic

For the following exercises, solve the equation for x .

3 ( x + 2 ) 12 = 5 ( x + 1 )

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12 5 ( x + 3 ) = 2 x 5

x = 2 7

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x 3 3 4 = 2 x + 3 12

x = 6

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3 ( 2 x 1 ) + x = 5 x + 3

x = 3

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2 x 3 3 4 = x 6 + 21 4

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Questions & Answers

If c is the cost function for a particular product, find the marginal cost functions and their values at x=10 a. c(x) = 800+ 0.04x + 0.0002x² b. c(x) = 250 + 100x + 0.001x²
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how to reduce an equation?
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by manipulation of both side
Al
9(y+8)-27 is 9y+45. Why can't you reduce that to y+5? I know that's wrong but can't explain why
Patrick Reply
when you reduce an equation to its simplest terms, you can't change the value of the equation. reducing it to y + 5 is equivalent to dividing it by 9 which changes the value. you can multiply it by 1 or 9/9 which would give 9(y + 5). multiplying it by one does not change the value.
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_3_2_1
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The denominator of a certain fraction is 9 more than the numerator. If 6 is added to both terms of the fraction, the value of the fraction becomes 2/3. Find the original fraction. 2. The sum of the least and greatest of 3 consecutive integers is 60. What are the valu
SABAL Reply
1. x + 6 2 -------------- = _ x + 9 + 6 3 x + 6 3 ----------- x -- (cross multiply) x + 15 2 3(x + 6) = 2(x + 15) 3x + 18 = 2x + 30 (-2x from both) x + 18 = 30 (-18 from both) x = 12 Test: 12 + 6 18 2 -------------- = --- = --- 12 + 9 + 6 27 3
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×/×+9+6/1
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Q2 x+(x+2)+(x+4)=60 3x+6=60 3x+6-6=60-6 3x=54 3x/3=54/3 x=18 :. The numbers are 18,20 and 22
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Mark and Don are planning to sell each of their marble collections at a garage sale. If Don has 1 more than 3 times the number of marbles Mark has, how many does each boy have to sell if the total number of marbles is 113?
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Mark = x,. Don = 3x + 1 x + 3x + 1 = 113 4x = 112, x = 28 Mark = 28, Don = 85, 28 + 85 = 113
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Practice Key Terms 7

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Source:  OpenStax, College algebra. OpenStax CNX. Feb 06, 2015 Download for free at https://legacy.cnx.org/content/col11759/1.3
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