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Graphs of Linear Equations in Two Variables

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Lesson Plans and Worksheets for Grade 8
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Videos to help Grade 8 students learn some facts about graphs of linear equations in two variables.

New York State Common Core Math Module 4, Grade 8, Lesson 21

Lesson 21 Student Outcomes

• Students write the equation of a line given two points or the slope and a point on the line.
• Students know the traditional forms of the slope formula and slope-intercept equation.

Lesson 21 Student Summary

The point-slope form of a linear equation is given by m(x2 - x1) = y2 - y1
Given a known (x, y), then the equation is written as m(x - x1) = y - y1
The following is slope-intercept form of a line: y = mx + b
In this equation, m is slope and b is the y-intercept.
To write the equation of a line you must have two points, one point and slope, or a graph of the line.

Lesson 21 Opening Exercise

Examples 1 - 4
Let a line l be given in the coordinate plane. What linear equation is the graph of line?
Exercises 1–5
1. Write the equation for the line l shown in the graph.
2. Write the equation for the line l shown in the graph.
3. Determine the equation of the line that goes through points (-4, 5) and (2, 3).
4. Write the equation for the line l shown in the graph.
5. A line goes through the point (8, 3) and has slope m = 4. Write the equation that represents the line.

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