Mario T.

asked • 11/02/15

Fnd the slope-intercept form of the line which passes through the given points.

Why is this wrong?
 
P(5,0) Q(0, -8)

m=(-8-0)/(0-5)

m=(-8-0(-1))/(0-5)

m=(-8+0)/(0-5)

m=(-8)/(-5)

Dividing two negatives equals a positive value

m=8/5
 
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My instructor keeps asking me --> y = mx+b where m is the slope and b is the y intercept. You found the slope m but what about b?  b is NOT given  :-(  Please help

David W.

Your answer so far is:   y = (8/5)x + b.          So, what is the value of b?
 
Andrew mentioned that the point (0,-8)  is the y-intercept (the point where x=0).  Michael described a general method for finding b using either point P or point Q.
 
So, actually, b was both given and you could compute it.
 
Next time, start with :) and impress your instructor (they live for such times).
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11/03/15

1 Expert Answer

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Michael J. answered • 11/02/15

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You only found the slope of the line that passes through the points.  Not the line.
 
 
y = mx + b
 
 
Plug in the slope and any of the given coordinate points into this equation to find b.
 
m = 8 / 5
 
Use the point (0, -8).
 
-8 = (8/5)(0) + b
 
-8 = b
 
 
The equation in slope-intercept form is
 
y = (8 / 5)x - 8
 
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Andrew M.

Since b is the y-intercept which is the point (0,b)
We were actually given the value of b in the original problem.
Since the line goes through (0,-8), which is the y-intercept, b=-8
 
Thus:  y = mx + b   becomes   y = (8/5)x-8
 
Had we not been given the value of b initially, then using Michael's
method to solve for b from a given point and slope works, but in
this case was unnecessary.
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11/03/15

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