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Find x if the slope between (7,-9) and (x,-13) is -1/3

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2 Answers

Recall that the slope, m, of a line between two points, (x1, y1) and (x2, y2), is given by the following formula:

          m = rise/run = (y2 - y1)/(x2 - x1

You are given the following:

          slope:   m = -1/3

          point 1:   (x1, y1) = (7, -9)

          point 2:   (x2, y2) = (x, -13)

You are asked to solve for x, which is represented by x2 in point 2. To do so, plug in all the given info into the slope formula and solve for the missing variable:

          m = (y2 - y1)/(x2 - x1

       -1/3 = (-13 - (-9))/(x - 7)

       -1/3 = (-4)/(x - 7)

      Cross multiply to get rid of the fractional expressions 

   -1(x - 7) = 3(-4)      

      Multiply each term inside parenthesis on left-hand side of equation by -1 

      -x + 7 = -12          

      Subtract 7 from both sides of the equation 

            -x = -19       

      Divide both sides of the equation by -1 to solve for x 

             x = 19 

Find x if the slope between (7,-9) and (x,-13) is -1/3

slope between two points:

slope = (y2 - y1)/(x2 - x1)

plug the given data from the problem and solve for x:

-1/3 = (-13 - (-9))/(x - 7)

-1/3 = (-13 + 9)/(x - 7)

-1/3 = (-4)/(x - 7)

cross -multiplying:

3(-4) = -1(x-7)

-12 = -x+7

-19 = -x

19 = x