Geometry Section 3.7 cont.“Writing Equations of Lines”

While the slope-intercept form for the equation of a line is very useful

in graphing, it is not nearly as useful for writing the equation of a line

(unless you happen to be given the slope and the y-intercept).

The point-slope form for the equation of a line is __________________

In this equation m is, again, the slope and x1 and y1 are ______________________

)( 11 xxmyy

line on the points any two

Example: Write an equation for the line in point-slope form.

1. slope of -1 and contains the point (-3, 9)

)3(19

)3(19

xy

xy

)( 11 xxmyy

Example: Write an equation for the line in point-slope form.

2. passes through the points (1, 4) and (-3, 8))( 11 xxmyy 1

4

4

13

48

m

)(1 11 xxyy )1(14 xy

Example: Write an equation for the line in point-slope form.

3. slope of 3 and a y-intercept of 15

)( 11 xxmyy

Example: Write an equation for the line in point-slope form.

4. passes through the point (5, 1) and is perpendicular to the line 2

3

5 xy

)( 11 xxmyy