[Tex/LaTex] Spacing in multiline equations

alignequationsspacing

Please help me to figure out how to produce with that:

I have the following code:

$$  gcd(0,0) = 0    $$
$$  gcd(u,v) = gcd(v,u) $$
$$  gcd(u,v) = gcd(-u,v) $$
$$  gcd(u,0) = |u| $$

$$
2^{x^3} = x+1/x\ge 2 = \pi\approx 3{,}14
$$

$$
x^{4357}+y^{4357}=z^{4357}
$$

This is what I need:

First requirement

I don't want to align anything, I just want to remove the space between equations because I think it takes too much space. Anyway I don't like the view of my equations, looks like something is not good there (only with gcd, the other equations looks OK). One thing to fix that is probably to use "\gcd" instead of "gcd"… I'd like to have some advice how to make it look better and to resolve the original question with spacing between equations as well. I also looking for the most simple solution, without using complex ams-structures if possible.

Best Answer

Actually, I've found a way. I started to use the following environment from "amsmath" packages: 

\begin{gather*}
    x + y = z \\
    x + z = y \\
    y + z = x \\
\end{gather*}

The following trick fixes the spacing between the equations inside:

\setlength{\jot}{2pt}

This trick fixes the spacing between text and equation for the both sides:

\abovedisplayskip=-10pt
\belowdisplayskip=-10pt

Now it looks so:

Image

And that is completely OK for me.

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