Hello,
We need first to know what's a gradient. The Gradient (also called Slope) of a straight line shows how steep a straight line is.
But how do we find the slope (or Gradient) from two points ?
For exemple, let's find the gradient of the two points PQ...
Method
1. We need the coordinates of the point P, and the point Q :
P = (6 ; -11)
Q = (k ; -9)
2. The slope is the change in height divided by the change in horizontal distance.
In other words we :
a) subtract the x values
b) subtract the y values
c) divide
Application for PQ
subtract x values : xQ - xP = k - 6
subtract the y values : yQ - yP = -9 - (-11) = -9 + 11 = 2
divide : (k-6) / 2
That is the gradient of PQ.. Now let us find the gradient of PR
Application for PR
subtract x values : xR - xP = 2k - 6
subtract the y values : yR - yP = -3 - (-11) = -3 + 11 = 8
divide : (2k-6)/8
That is the gradient of PR.
We know that by assumption, gradient of PQ = gradient of PR, what is the value of k ? Well, we simply need to solve an equation here :
gradient of PQ = gradient of PR
(k-6) / 2 = (2k - 6) / 8
k-6 = (4k - 12)/8 (we have multiplied by 2 on each sides of the equation)
8k - 48 = 4k - 12 (we have multiplied by 8 on each sides of the equation)
8k - 4k = - 12 + 48
4k = 36
k = 36 / 4 = 9
So the value of k in order for the two gradients to be equals needs to be equal to 9
Good luck