writing the equation of line given two points
TRANSCRIPT
Writing the Equation of
a Line
Slope-intercept and Standard Forms
Objective: Given two points, write the equation of a
line in both slope-intercept and standard forms.
Standard Form
Point-Slope Form
m is the slope (x1, y1) is one of the points on the line.
Example Write the equation of the line that
passes through the points (1, 4) and (-2, -5) in both slope-intercept and standard forms.
First, find the slope. (CC BY-NC 2.0)
Use Point-Slope Form Use m=3 and one point. We will choose
(1,4).
This is the slope-intercept form of the line.
Distribute
Add 4 to both sides
Simplify
Now solve for y…
Standard Form (Ax+By = C)
Three Conditions: There are no fractions. The leading coefficient, A, is positive. A, B, and C have no common factors.
Write the equation in standard form (Ax+By = C)
Subtract 3x on both sides
This matches Ax+By = C
Next step: Check the 3 conditions…
Check the Conditions…
Three Conditions: There are no fractions – This condition is already
met. The leading coefficient, A, is positive – multiply
both sides of the equation by -1.
A, B, and C have no common factors – This condition is already met.
Final Answer! Equation in standard form:
The Graph…just for fun Here is the graph
of y=3x+1 You can see that
the line passes through our original points (1,4) and (-2, -5)
Photo Credit
The photo “Downhill Skiing in Kajaani, Finland” is © 2005 Visit Finland, used under a Creative Commons Attribution-NonCommercial 2.0 Generic license: http://creativecommons.org/licenses/by-nc/2.0/deed.en