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| Math Central | Quandaries & Queries |
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Subject: Slope-intercept and graphing Hey, I'm really confused with this, tried to figure it out on my own but i can't seem to grasp it here's the problem: b. (has a coordinate plane to graph points) if you could help me with this I would be most appreciative! |
Hi Anthony,
I am going to use two different points, (-3, -1) and (3, 2). The slope-intercept form of a line is
y = mx + b
where m is the slope and b is the y-intercept.
First find the slope m.
m = (y2 - y1)/ (x2 - x 1) = (2 - (-1))/(3 - (-3)) = (2 + 1)/(3 + 3) = 3/6 = 1/2
So the equation is
y = 1/2 x + b
To find b substitute one of the two points into the equation. I am going to use (3, 2), thus
2 = 1/2 (3) + b so b = 2 - 3/2 = 1/2
Thus the equation of the line in slope-intercept form is
y = 1/2 x + 1/2
To plot the graph you already know the y-intercept, 1/2, so the point (0, 1/2) is on the graph. To find another point let y = 0 and you get
0 = 1/2 x + 1/2
so x = -1. Thus (-1, 0) is on the graph.
Plot these two points in the plane and then use a ruler to draw the line.
I also plotted the original points and they do lie on the line.
Penny
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