Apologies if I’m off forum. Nothing seemed to fit.
I recently educated myself on how to find the intersection of two lines and I’ve been stumped by a certain formula found at http://www.euclideanspace.com/maths/geometry/elements/intersection/twod/index.htm.
There the formula for y-intersect, when two points of a line are known, is presented as:
b = (B.x*A.y - A.x*B.y)/(B.x - A.x)
I follow the author’s algebra, terse as it is, all the way from the basic line-formula right up to the formula for slope:
m = (B.y - A.y)/(B.x - A.x)
But I don’t see what he’s done from this point to bring about this 2-point formula for y-intercept, and he doesn’t bother trying to explain.
I can see that the numerator of slope has been inverted and multiplied by the x values of A and B, but I haven’t been able to understand, algebraically, why. So the answer I’m looking for would bridge the gap in these formulas in a plain, step by step, fashion. Thanks.
