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Homework Help: Find slope of line, two points on the line are included

  1. Dec 7, 2012 #1
    1. The problem statement, all variables and given/known data

    find the slope of this line it contains these points:

    (-16, -1) , (-17, -7)

    2. Relevant equations

    y = mx + b

    3. The attempt at a solution

    i got y = 3/8x - .625

    is that correct?

    my work i use -7 +1 / -17 + 1

    ==-6/16


    ==6/16 = 3/8

    then i used -7 = 3/8 * -17 + b

    =6.375
     
  2. jcsd
  3. Dec 7, 2012 #2

    Mentallic

    User Avatar
    Homework Helper

    Not quite, you got the gradient wrong. In the formula

    [tex]m=\frac{y_2-y_1}{x_2-x_1}[/tex]

    You mistakenly substituted y1 a second time where x1 is instead meant to be.

    Also, your technique to find the missing value of b works, but you might also be interested to know that there is a formula for a line that has gradient m and passes through the point (x0,y0) as

    [tex]y-y_0=m(x-x_0)[/tex]

    And if we divide both sides by x-x0, you may see it is quite similar to the gradient formula:

    [tex]m=\frac{y-y_0}{x-x_0}[/tex]
     
  4. Dec 8, 2012 #3
    thankyou upon checking my work, i got the m = 6

    and the b = 95

    and I also used the new point slope formula, thanks.
     
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