SOLUTION: if the points (3, r) and (r, -1) lie on a line with slope -3/4, wat is the value of r?

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Question 249778: if the points (3, r) and (r, -1) lie on a line with slope -3/4, wat is the value of r?
Answer by mathhub(11) About Me  (Show Source):
You can put this solution on YOUR website!
The coordinates of two points connecting the line are given.
Let's say the 2 points are denoted as A and B. Let us assign the coordinates (3, r) topoint A and coordinates (r, -1) to point B.
The slope of the line is given by the difference of the y-coordinates over the difference of x-coordinates of points A and B.
Thus the slope is given by %28r%2B1%29%2F%283-r%29
But then as per the question the slope of the line is -3/4. That means
%28r%2B1%29%2F%283-r%29 = -3%2F4
=> 4(r+1) = -3(3-r)
=> 4r + 4 = -9 + 3r
=> 4r - 3r = -9 - 4
=> r = -13
Therefore the value of r is -13.