Mrs. Agriesti's Algebra I Notes
5.3 Write Equations of Lines Given two Points
Objective:
To use two points to write the equation of a line.
Notes:
Slope Formula:
Steps to finding the equation:
- Write "y = mx + b".
- Find the slope. (For help see section 4.4).
- Replace the variable m with the slope you found in step 2.
- Choose one of your points. Make note of its coordinates.
- Replace the variable x with the x-coordinate of the point from step 4 and y with the y-coordinate of the point.
- Solve for the only variable you have left, b.
- Write "y = mx + b" again.
- Replace m with the slope and b with the value you found in step 6.
Examples:
Solve:
- Write the equation of the line containing the points (−1, 1) and (0, 3).
- Write the equation of the line containing the points (4, 4) and (−2, −1).
- Write the equation of the line containing the points (3, −4) and (3, 8).
