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math doubt | Reply
why A = Y2 - Y1 in second page?
Re: math doubt (response to post by kai_stauch) | Reply
If the line in question goes through two points (x1,y1) and (x2,y2) we can write

Ax1 + By1 = C
Ax2 + By2 = C

Subtracting second from first we get

A(x1-x2) + B(y1-y2) = 0

or

A(x1-x2) = B(y2-y1)

The easiest way to make both sides equal is to substitute
A = y2-y1 and B = x1-x2
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