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The Various Forms of a Linear EquationLearning mathematics is very much like the construct...

The Various Forms of a Linear Equation

Learning mathematics is very much like the construction of a skyscraper. The final height of the skyscraper ultimatel depends on the strength of the foundation and quality of the frame supporting each new floor as it is built. Our previous work with linear functions and their graphs, while having a number of useful applications, is actually the foundation on which much of our future work is built. For this reason, it’s important you gain a certain fluency with linear functions and relationships—even to a point where things come to you effortlessly and automatically. As noted mathematician Henri Lebesque once said, “An idea reaches its maximum level of usefulness only when you understand it so well that it seems like you have always known it. You then become incapable of seeing the idea as anything but a trivial and immediate result.” These formulas and concepts, while simple, have an endless number of significant and substantial applications.

Forms and Formulas

slope formula

point-slope form

slope-intercept form

standard form

yy1 = m(xx1)

y = mx + b

Ax + By = C

given any two points on the line

given slope m and any point (x1, y1)

given slope m and y-intercept (0, b)

A, B, and C are integers (used in linear systems)

Characteristics of Lines

y-intercept

x-intercept

increasing

decreasing

(0, y)

(x, 0)

m > 0

m > 0

let x = 0, solve for y

let y = 0, solve for x

line slants upward from left to right

line slants downward form left to right

Relationships between Lines

intersecting

parallel

perpendicular

dependent

m1m2

m1 = m2,

b1b2

m 1m2 = − 1

m 1 = m2, b1 = b2

lines intersect at one point

lines do not intersect

lines intersect at right angles

lines intersect at all points

Special Lines

Horizontal

vertical

identity

y = k

x = h

y = x

horizontal line through k

vertical line through h

the input value identifies the output

Use the formulas and concepts reviewed here to complete the following exercises.

For the two points given: (a) compute the slope of the line through the points and state whether the line is increasing or decreasing, (b) find the equation of the line in point-slope form, then write the equation in slope-intercept form, and (c) find the x- and y-intercepts and graph the line.

P1(− 2, 5) P2(6,−1)

Step-by-Step Solution

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