Bob B.

asked • 05/18/15

A line passes through point (-3,1) and has a slope of -3.

I don't know how to figure this out and get it into y=mx+b form. Any help is appreciated.
 
 

Lisa G.

what does it mean WHEN ASKED which equation represents the line that passes through (1,-3) (-2, 3)? how do I figure this out? A. y= -2x -1
             B. y= -2x + 5
             C. y= -0.5x - 2.5
             D. y= -0.5x + 2
 I just need help to figure out what its asking me to do. or a web site that I can learn linear equations?
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02/19/16

Andrew M.

When given two points and you need to find the equation of the line
the first step is to find the slope m.
 
m = rise/run or  (y2-y1)/(x2-x1) = (3-(-3))/(-2-1) = 6/(-3) = -2
 
You now have the slope and 2 points.  You can use either point
and the slope to plug into the slope intercept form
y-y1 = m(x-x1)
 
Let's use (1,-3) along with our slope of -2
 
y-(-3) = -2(x-1)
y+3 = -2x + 2
y = -2x -1
 
Your answer is A
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02/20/16

1 Expert Answer

By:

Andrew M. answered • 05/19/15

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You need to use the point slope formula:   y-y1 = m(x-x1)
The slope is m given as m=-3
The point given on the line (-3,1) is (x1,y1)  so x1 = -3, y1 = 1
 
Just plug into the formula
 
y-1 = -3(x-(-3))
y-1 - -3(x+3)
y-1 = -3x - 9
now add 1 to both sides giving
y = -3x -8
 
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