Chapter 2.4

Writing Linear Equations

By the end of this lesson you will be able to:

Write an equation in slope-intercept form when given:

slope and a y-intercepta point and the slopetwo points

Write an equation of a parallel line Write an equation of a perpendicular line

Slope-Intercept Form:

Y = mx + b

M = slope of the lineB = y-intercept

Writing equations of Lines:

Given slope of -8 and passes through (2,4)

Take the equation y=mx+b and substitute the -8 in for “m”

Y = (-8)x + bTo find the value of “b” – take the value of x and

y from the point and substitute(4) = (-8)(2) +b b = 20Y = -8x + 20

You Try!

Write the equation of the line with a slope of 3 and passing through (0, -5).

Equations – given two points:

Given two points (4,1) and (7,7)

Find the slope using the slope formula

Plug 2 in for “m”Pick one of the points to get

the values for the x and yOnce you get the value for “b”

then rewrite the equation

Y = 2x - 7

47

17

m

(1) = (2)(4) + b

b = -7

You Try!

Write the equation of the line that passes through the points (4, 8) and (-2, 10).

Parallel Lines:

Parallel Lines have the same slope

Write an equation that is parallel to y=3x+2 and passes through (0,2)

The new line would have the same slope, so m=3

Take the x and y from the point and find “b”

You Try!Write an equation that is parallel to

y=1/2x + 4 and passes through (-8, 3)

Perpendicular Lines:

Perpendicular Lines have slopes that are opposite-reciprocal

Write an equation that is perpendicular to y= -½x +2 and passes through (8,2)

The new line’s slope would be 2Take the x and y value to find bThen rewrite the new equation

You Try!

Write and equation that is perpendicular to

y = - 1/3x – 4 and passes through (2, 5)

Tonight’s Homework:

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(23-37 odd)