# What's the point in the general form of a plane equation?

So I've been reading up on my maths (Mathematics for Computer Graphics by John Vince FYI) and come to analytic geometry and I have a question.

Why define the Cartesian form of a plane equation as: $$ax + by + cz - d = 0$$ To then define the general form as: $$Ax + By + Cz + D = 0$$ Where $$A = a$$ $$B = b$$ $$C = c$$ $$D = -d$$

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Plus signs are just more positive ;-) –  vonbrand Mar 23 '14 at 22:58
Jest aside, using uniform signs gives more regular results. and is easier to remember. –  vonbrand Mar 23 '14 at 22:59
I think it adds more confusion. I've seen multiple articles around the internet that talk about the general form, but never reference that $$D = -d$$. The way the Cartesian form is defined really makes sense and there's a reason why it is $$-d$$, why disregard it? –  Soapy Mar 23 '14 at 23:11
Whatever form you prefer, state it clearly and stick to it. It is completely arbitrary, in the end. –  vonbrand Mar 23 '14 at 23:14