Mathematics
Grade 8
15 min
Graph a line using slope
Graph a line using slope
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1
Introduction & Learning Objectives
Learning Objectives
Identify the slope and y-intercept from a linear equation in slope-intercept form.
Plot the y-intercept on a coordinate plane.
Use the slope (rise over run) to find at least two additional points on a line.
Accurately draw a straight line through the plotted points.
Graph a linear equation given in slope-intercept form ($y = mx + b$).
Interpret the direction and steepness of a line based on its slope.
Ever wonder how roller coasters are designed to go up and down at just the right angle? 🎢 It all comes down to understanding 'slope'!
In this lesson, you'll learn a powerful method to draw straight lines on a graph using two key pieces of information: the slope and the y-intercept. This skill is fundamental for understanding how linear relat...
2
Key Concepts & Vocabulary
TermDefinitionExample
Coordinate PlaneA two-dimensional surface formed by two perpendicular number lines, the x-axis (horizontal) and y-axis (vertical), used to locate points.The grid paper you use for graphing is a coordinate plane, with the point (0,0) at its center.
Linear EquationAn equation whose graph is a straight line. It typically involves two variables, like x and y, raised to the first power.$y = 2x + 3$ is a linear equation.
Slope (m)A measure of the steepness and direction of a line. It describes how much the line rises or falls vertically for every unit it moves horizontally.A slope of 2 means the line goes up 2 units for every 1 unit it goes right.
Y-intercept (b)The point where a line crosses the y-axis. At this point, the x-coordinate is always 0.In the equation $y = 2x +...
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Core Formulas
Slope-Intercept Form
$y = mx + b$
This is the standard form for a linear equation where 'm' represents the slope of the line and 'b' represents the y-intercept (the point where the line crosses the y-axis, (0, b)).
Slope Formula (Rise over Run)
$m = \frac{\text{rise}}{\text{run}} = \frac{\text{change in y}}{\text{change in x}}$
This formula defines slope as the ratio of the vertical change (rise) to the horizontal change (run) between any two points on a line. A positive slope means the line goes up from left to right, and a negative slope means it goes down.
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Challenging
A common mistake is confusing 'rise' and 'run'. If a student tries to graph y = 2/3x + 4 by starting at (0, 4) and then moving right 2 and up 3, which incorrect equation are they actually graphing?
A.y = 3/2x + 4
B.y = 2/3x - 4
C.y = -2/3x + 4
D.y = 4x + 2/3
Challenging
The slope of a line is -5/3. Which of the following describes two valid but different movements from a point to find another point on the same line?
A.(Down 5, Right 3) and (Down 5, Left 3)
B.(Up 5, Right 3) and (Down 5, Left 3)
C.(Down 5, Left 3) and (Up 5, Right 3)
D.(Down 5, Right 3) and (Up 5, Left 3)
Challenging
Which linear equation, when graphed, would create a line passing through both (-4, 5) and (2, -1)?
A.y = x + 9
B.y = -x + 1
C.y = -1/2x + 3
D.y = 2x + 13
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