Math CentralQuandaries & Queries


Subject: Slope-intercept and graphing
Name: Anthony
Who are you: Student

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:
Two points are given
a. Write an equation in slope-intercept form for the line containing the two points.
b. Graph the line from Part a and check that both points are on the line.
a.= (-3, 7) and (5, -1)

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.


About Math Central


Math Central is supported by the University of Regina and The Pacific Institute for the Mathematical Sciences.
Quandaries & Queries page Home page University of Regina PIMS