00:01
We're going to show that the parametric equation, x is equal to x1 plus x2 minus x1t, and y equals y1 plus y2 minus y1 t for t between zero on one.
00:15
We're going to show that this parameterizes the line segment from x1 y1 to x2 y2.
00:23
So first off, let's solve for t in both equations.
00:28
In the equation for x, we get t is equal to x minus x1 over x2 minus x1.
00:39
And in the equation for y, we get t is equal to y minus y1 over y2 minus y1, setting both of these equal to each other.
00:55
We then get x minus x1 over x2 minus x1 is equal to y minus y1 over y2 minus y1 over y2 minus y1 okay now we can rearrange a little bit remember that the slope of a line between the points x1 y1 and x2 y2 is equal to y2 minus y1 over x2 minus x1.
01:28
In other words, it's rise over run.
01:32
Well, we have y2 minus 1 and x2 minus x1 over here.
01:36
So if we multiply by y2 minus y1 on both sides, then we get y2 minus y1 over x2 minus x1 times x minus x1 is equal to y minus y 1.
01:58
And now if we substitute m for this, that is m times x minus x1 is equal to y minus y 1.
02:10
This is one of the forms of the equation for a straight line between the points x1, y1, and x2, y2...